**EXHIBIT 15.1**

 

The Boardof Directors and Stockholders of Rigel Pharmaceuticals, Inc.

 

We are aware of the incorporation by reference in thefollowing Registration Statements:

 
| (1)    |   | Form S-3ASR  No. 333-148838, of Rigel Pharmaceuticals, Inc.                                                                                                                                                                                                                                                                                                                        |
|--------|--------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| (2)    |   | Form S-3  No. 333-129650, of Rigel Pharmaceuticals, Inc.                                                                                                                                                                                                                                                                                                                           |
| (3)    |   | Form S-3  No. 333-119785, of Rigel Pharmaceuticals, Inc.                                                                                                                                                                                                                                                                                                                           |
| (4)    |   | Form S-3  No. 333-112746, of Rigel Pharmaceuticals, Inc.                                                                                                                                                                                                                                                                                                                           |
| (5)    |   | Form S-3  No. 333-111777, of Rigel Pharmaceuticals, Inc.                                                                                                                                                                                                                                                                                                                           |
| (6)    |   | Form S-3  No. 333-106942, of Rigel Pharmaceuticals, Inc.                                                                                                                                                                                                                                                                                                                           |
| (7)    |   | Form S-3  No. 333-105431, of Rigel Pharmaceuticals, Inc.                                                                                                                                                                                                                                                                                                                           |
| (8)    |   | Form S-3  No. 333-87276, of Rigel Pharmaceuticals, Inc.                                                                                                                                                                                                                                                                                                                            |
| (9)    |   | Form S-3  No. 333-74906, of Rigel Pharmaceuticals, Inc.                                                                                                                                                                                                                                                                                                                            |
| (10)   |   | Form S-8 No. 333-148132, pertaining to the 2000  Equity Incentive Plan, 2000 Employee Stock Purchase Plan and 2000  Non-Employee Directors’ Stock Option Plan of Rigel Pharmaceuticals, Inc.                                                                                                                                                                                  |
| (11)   |   | Form S-8  No. 333-139516, pertaining to the 2000 Employee Stock Purchase Plan of  Rigel Pharmaceuticals Inc.                                                                                                                                                                                                                                                                            |
| (12)   |   | Form S-8  No. 333-134622, pertaining to the 2000 Equity Incentive Plan and 2000  Employee Stock Purchase Plan of Rigel Pharmaceuticals, Inc.                                                                                                                                                                                                                                       |
| (13)   |   | Form S-8  No. 333-125895, pertaining to the 2000 Equity Incentive Plan, 2000  Employee Stock Purchase Plan and 2000 Non-Employee Directors’ Stock Option  Plan of Rigel Pharmaceuticals, Inc.                                                                                                                                                                                 |
| (14)   |   | Form S-8  No. 333-111782, pertaining to the 2000 Equity Incentive Plan of Rigel  Pharmaceuticals, Inc.                                                                                                                                                                                                                                                                             |
| (15)   |   | Form S-8  No. 333-107062, pertaining to the 2000 Employee Stock Purchase Plan of  Rigel Pharmaceuticals, Inc.                                                                                                                                                                                                                                                                      |
| (16)   |   | Form S-8  No. 333-106532, pertaining to the 2000 Equity Incentive Plan, 2000  Employee Stock Purchase Plan and 2000 Non-Employee Directors’ Stock Option  Plan of Rigel Pharmaceuticals, Inc.                                                                                                                                                                                 |
| (17)   |   | Form S-8  No. 333-72492, pertaining to the 2001 Non-Officer Equity Incentive Plan  of Rigel Pharmaceuticals, Inc.                                                                                                                                                                                                                                                                  |
| (18)   |   | Form S-8  No. 333-51184, pertaining to the 2000 Equity Incentive Plan, 2000  Employee Stock Purchase Plan and 2000 Non-Employee Directors’ Stock Option  Plan of Rigel Pharmaceuticals, Inc.                                                                                                                                                                                  |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                              |
|   |   | in each  case related to the sale of shares of common stock, and in the related  prospectuses, as applicable, contained in such Registration Statements of our  report dated, October 31, 2008 relating to the unaudited interim condensed  financial statements of Rigel Pharmaceuticals, Inc. that are included in  its Form 10-Q for the quarter ended September 30, 2008. |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                              |
|   |   | Pursuant to Rule 436(c) of the Securities Act  of 1933, our report is not a part of the registration statements prepared or  certified by accountants within the meaning of section 7 or 11 of the  Securities Act of 1933, as amended.                                                                                                                                                 |

 

 
|                        | /s/  Ernst & Young LLP |
|------------------------|---------------------------------|
|                   |                            |
|                   |                            |
| Palo  Alto, California |                            |
| October 31,  2008 |                            |

 

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