Following Gottschalk v. Benson in 1972 and Parker v. Flook in 1978, the U.S. Supreme Court again had the opportunity to consider 35 USC section 101 in Diamond v. Chakrabarty in 1980. The Court held that a patent claim for a live, human-made microorganism is patentable subject matter as either a manufacture or composition of matter under 35 USC section 101.
The counsel for the patent applicant argued, in part, that because the USPTO had recognized microorganisms as a unique subclassification in its classification system and had issued at least 60 patents for microorganisms that the PTO had already recognized microorganisms as being patentable. You can hear part of that argument [here].
Interestingly, the USPTO just recently published a PowerPoint presentation on business methods. It is available [here]. In this presentation, the USPTO recognizes that it issued 1600 business methods in 2008. Assuming the PTO issues roughly 157,800 patents every year, the 1600 patents accounted for only 1.0% of all patents issued by the USPTO.
You can listen to the entire oral argument in Diamond v. Chakrabarty [here].
You can read the Court’s opinion [here].