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                                                                    EXHIBIT 4.33

[PROTHERICS LOGO]

23 February 2004

Dr John Brown
17 Blackford Road
Edinburgh
EH9 2DT

Dear John

               PROTHERICS PLC (THE "COMPANY") AND YOUR APPOINTMENT
                    TO THE BOARD AS A NON-EXECUTIVE DIRECTOR

Following the recommendation of the nomination committee, the board of the
Company (the "BOARD") is pleased to hear that you have accepted our offer to
join on the Board as a non-executive director with effect from 1 March 2004.
This letter confirms the main terms of your appointment to this office. You
should be aware that your appointment will have to be ratified by the Company's
shareholders at the annual general meeting in July 2004 and is subject to the
Company's articles of association as amended from time to time. If there is a
conflict between the terms of this letter and the articles of association then
the articles shall prevail.

DUTIES

1.    You will be informed how the Board is structured and what authorities are
      delegated to the Chief Executive and his colleagues.

2.    The Board as a whole is collectively responsible for promoting the success
      of the Company by directing and supervising the Company's affairs. The
      Board's role is to:

      (a)   provide entrepreneurial leadership to the Company within a framework
            of prudent and effective controls which enable risk to be assessed
            and managed;

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      (b)   set the Company's strategic aims, ensure that the necessary
            financial and human resources are in place for the Company to meet
            its objectives, and review management performance; and

      (c)   set the Company's values and standards and ensure that its
            obligations to its shareholders and others are understood and met.

3.    In your role as a non-executive director you are required (with the other
      non-executives) to:

      (a)   constructively challenge and contribute to the development of
            strategy;

      (b)   scrutinise the performance of management in meeting agreed goals and
            objectives and monitor the reporting of performance;

      (c)   satisfy yourself that financial information is accurate and that
            financial controls and systems of risk management are robust and
            defensible;

      (d)   be responsible for determining appropriate levels of remuneration of
            executive directors and have a prime role in appointing, and where
            necessary removing, senior management and in succession planning.

4.    You will be required to:

      (a)   exercise relevant powers under the Company's memorandum and articles
            of association;

      (b)   perform your duties faithfully, efficiently and diligently and use
            all reasonable endeavours to promote the interests and reputation of
            the Company;

      (c)   comply with your fiduciary duties;

      (d)   report the wrongdoing (including acts of misconduct, dishonesty,
            breaches of contract, fiduciary duty, company rules or the rules of
            the relevant regulatory bodies) whether committed, contemplated or
            discussed by any other director or member of staff of the Company
            and any group company of which you were aware to the Board
            immediately, irrespective of whether this may involve some degree of
            self incrimination;

      (e)   serve on the audit, nomination and remuneration committees of the
            Board and attend, wherever possible, all meetings of the committees
            (committee meetings may occasionally be scheduled separately from
            Board meetings);

      (f)   attend all general meetings of the Company;

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      (g)   attend, wherever possible, all meetings of the Board, which meets on
            an agreed schedule (in 2004, 10 meetings are scheduled). These are
            mostly at the Company's offices at Ludgate Hill, London, with
            occasional meetings at other Company locations;

      (h)   consider all relevant papers in advance of each meeting in order to
            ensure that you can play a full part in the work of the Board and
            its committees;

      (i)   bring independent judgement to bear on issues of strategy, policy,
            resources, performance and standards of conduct;

      (j)   make yourself available (on reasonable notice) to provide ad hoc
            advice to individual directors of the Company;

      (k)   provide guidance and direction in planning, developing and enhancing
            the future strategic direction of the Company;

      (l)   share responsibility with the other directors for the effective
            control of the Company and with the other non-executive directors
            for the supervision of the executive directors; and

      (m)   comply with the Financial Services Authority's Model Code for
            securities transactions by directors of listed companies and with
            any code of conduct relating to securities transactions by directors
            and specified employees issued by the Company from time to time.

5.    Overall the Company anticipates that you will need to spend an average of
      one day per month fulfilling your duties after the induction phase. This
      will include the board meetings, annual general meetings, annual strategy
      meeting and site visits. In addition you will be expected to spend an
      appropriate period of time preparing for each meeting. By accepting this
      appointment you confirm that you are able to commit sufficient time to the
      role to meet the Company's expectations.

6.    The Company seeks to adhere to the principles in the Cadbury Report on
      Corporate Governance, the Greenbury Report on Directors' Remuneration, the
      Hampel Report on Corporate Governance and the Turnbull Report on Internal
      Control. You will be expected to carry out your duties in accordance with
      the principles set out in these reports, copies of which are available
      from the Company Secretary.

7.    The performance of the Board and its committees, and of individual
      directors, is evaluated annually.

8.    You shall, in pursuance of your duties hereunder, be entitled to request
      such information from the Company, its subsidiary undertakings (as defined
      in section 258 of the Companies Act 1985 as amended from time to time) or
      its or their employees, consultants or professional advisers as may be
      reasonably necessary to enable you to perform your role effectively. The
      Company shall use its reasonable endeavours to

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      provide such information promptly.

CONFIDENTIALITY

During the course of your duties you will have access to confidential
information belonging to the Company and its subsidiary undertakings (including,
but not limited to, details of suppliers, customers, margins, know-how,
marketing and other relevant business information). Unauthorised disclosure of
this information could seriously damage the Company. You therefore undertake not
to use or disclose such information save in pursuance of your duties or in
accordance with any statutory obligation or court or similar order.

Your attention is drawn to the rules relating to the disclosure of price
sensitive information. You must not make any statement or do anything which may
be a breach of these rules without prior clearance from the Chairman or Company
Secretary.

OUTSIDE INTERESTS

The agreement of the chairman should be sought before you accept any new outside
interests which might affect the time you are able to devote to this
appointment.

In accordance with the principles set out in the Combined Code you must inform
the Board of any interests which you have, or acquire, which might reasonably be
thought to jeopardise your independence from the Company.

During your appointment you most not take up any office or employment with, or
have any interest in, any firm or company which is or may be in direct or
indirect competition with the Company.

The Board have determined you to be independent, according to the provisions of
the Combined Code.

INSURANCE

During your appointment you will be covered by the Company's directors' and
officers' liability insurance on the terms currently in place for the rest of
the Board. The current indemnity limit is (pound)10 million. A copy of the
policy document is available from the Company Secretary. The Company does not
guarantee to maintain this insurance cover after the termination of your
appointment, but you will continue to be covered by the policy or any
replacement on the same basis as the rest of the Board.

APPOINTMENT

Your appointment will commence on 1 March 2004 and is terminable by three
months' notice from either the Company or yourself. It is envisaged that your
appointment will initially be for a term of three years. The continuation of
your appointment depends upon satisfactory performance and re-election at
forthcoming Annual General Meetings.

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Not withstanding the aforementioned notice provisions, the Company may terminate
your appointment with immediate effect if you have:

(a)   committed any serious breach or (after warning in writing) any repeated or
      continued material breach of your obligations to the Company (which
      include an obligation not to breach your fiduciary duties);

(b)   been guilty of any act of dishonesty or serious misconduct or any conduct
      which (in the reasonable opinion of the Board) tends to bring you or the
      Company into disrepute; or

(c)   been declared bankrupt or have made an arrangement or composition with of
      for the benefit of your creditors,

or for any other reason set out in the Company's articles of association.

All appointments and reappointments to the Board are, of course, subject to the
Company's articles of association. If you are not re-elected to your position as
a director of the Company by the shareholders at any time and for any reason
then this appointment shall terminate automatically and with immediate effect.

On termination of the appointment you shall only be entitled to such fees as may
have accrued to the date of termination together with reimbursement in the
normal way of any expenses properly incurred prior to that date.

REMUNERATION

The fee is (pound)21,000 per annum (subject to income tax and statutory
deductions) and is payable monthly in arrears. The company will be reviewing
remuneration within the next few months. If you undertake any special duties
beyond those specified in this letter you will not receive any additional
payment unless agreed with the Board in advance.

EXPENSES

The Company will reimburse you for any expenses that you may incur properly and
reasonably in performing your duties and which are properly documented. Such
expenses would include reasonable legal fees if circumstances should arise in
which it was necessary for you to seek separate legal advice about the
performance of your duties. In such a situation, you are required to discuss the
issue either with me or with one of your non-executive colleagues in advance.

INDEPENDENT PROFESSIONAL ADVICE

In some circumstances you may think that you need professional advice in the
furtherance of your duties as a director. It may also be appropriate for you to
seek advice from independent advisers at the Company's expense. A copy of the
Board's agreed procedure under which directors may obtain such independent
advice is available from the Company Secretary. The

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Company will reimburse the full cost of any expenditure incurred in accordance
with the policy.

DATA PROTECTION

By signing this agreement you consent to the Company holding and processing
information about you which you may provide or which it may acquire during the
course of this agreement, providing such use is in accordance with the Data
Protection Act 1998. In particular you consent to the Company holding and
processing:

(a)   personal data relating to you, for administrative and management purposes;
      and

(b)   "sensitive personal data" relating to you (as defined in the Data
      Protection Act 1998) including, for example:

            (i)   your health records and any medical reports given to or
                  obtained by the Company, for monitoring sick leave and taking
                  decisions as to your fitness to work;

            (ii)  your racial or ethnic origin (in order to monitor compliance
                  with the Race Relations Act 1976);

            (iii) any information relating to criminal proceedings in which you
                  have been involved for compliance with the Company's legal or
                  regulatory requirements, for insurance purposes, and in
                  relation to its obligations to third parties.

You also consent to the Company making such information available to:

(a)   its group companies, offices and (if necessary) customers outside the
      European Economic Area in order to further its business interests; and

(b)   its group companies, its offices, those who provide products or services
      to the Company, regulatory authorities, governmental or quasi governmental
      organisations and potential purchasers of the Company or its business.

THIRD PARTY RIGHTS

The Contracts (Rights of Third Parties) Act 1999 shall not apply to this
agreement No person other than the parties to this agreement and any group
company shall have any rights under it and it will not be enforceable by any
person other than those parties.

Please sign and return the enclosed copy of this letter to confirm your
agreement to the above terms. We will separately also ask you to sign a form 288
for filing at Companies House.

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The Company looks forward to working with you in the future.

Yours sincerely

/s/ Stuart Wallis
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Stuart Wallis
for and on behalf of Protherics PLC

I agree to the above terms of appointment as a non-executive director of
Protherics PLC.

/s/ Dr. John Brown
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Dr. John Brown

Date 25th Feb 2004

In the presence of:

Witness signature:   /s/ Carol G. Brown
Witness name:        Carol G. Brown
Witness address:     17 Blackford Road, EDINBURGH EH9 2DT
Witness occupation: