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(Slip Opinion) 

OCTOBER  TERM,  2011 

1 

Syllabus 

NOTE:  Where  it  is  feasible,  a  syllabus  (headnote)  will  be  released,  as  is
being  done  in  connection  with  this  case,  at  the  time  the  opinion  is  issued.
The  syllabus  constitutes  no  part  of  the  opinion  of  the  Court  but  has  been
prepared  by  the  Reporter  of  Decisions  for  the  convenience  of  the  reader. 
See United States v. Detroit Timber & Lumber Co., 200 U. S. 321, 337. 

SUPREME COURT OF THE UNITED STATES 

Syllabus 

MAYO COLLABORATIVE SERVICES, DBA MAYO 

MEDICAL LABORATORIES, ET AL. v. PROMETHEUS 

LABORATORIES, INC. 

CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR 
THE FEDERAL CIRCUIT 

No. 10–1150.  Argued December 7, 2011—Decided March 20, 2012 

Although “laws of nature, natural phenomena, and abstract ideas” are
not patentable subject matter under §101 of the Patent Act, Diamond 
v. Diehr, 450 U. S. 175, 185, “an application of a law of nature . . . to 
a known structure or process may [deserve] patent protection,” id., at 
187.  But to transform an unpatentable law of nature into a patent-
eligible application of such a law, a patent must do more than simply
state  the  law  of  nature while  adding  the words  “apply  it.”    See,  e.g., 
Gottschalk v. Benson, 409 U. S. 63, 71–72.  It must limit its reach to a 
particular, inventive application of the law. 
  Respondent,  Prometheus  Laboratories,  Inc.  (Prometheus),  is  the 
sole and exclusive licensee of the two patents at issue, which concern 
the use of thiopurine drugs to treat autoimmune diseases.  When in-
gested, the body metabolizes the drugs, producing metabolites in the
bloodstream.    Because  patients  metabolize  these  drugs  differently,
doctors have found it difficult to determine whether a particular pa-
tient’s dose is too high, risking harmful side effects, or too low, and so 
likely ineffective.  The patent claims here set forth processes embody-
ing  researchers’  findings  that  identify  correlations  between  metabo-
lite  levels  and  likely  harm  or  ineffectiveness  with  precision.    Each 
claim recites (1) an “administering” step—instructing a doctor to ad-
minister  the  drug  to  his  patient—(2)  a  “determining”  step—telling
the doctor to measure the resulting metabolite levels in the patient’s
blood—and  (3)  a  “wherein”  step—describing  the  metabolite  concen-
trations above which there is a likelihood of harmful side-effects and 
below  which  it  is  likely  that  the  drug  dosage  is  ineffective,  and  in-
forming  the  doctor  that  metabolite  concentrations  above  or  below