In 1992, Thailand amended its Patent Act in order to ensure compliance with TRIPS, which significantly increased the level of pharmaceutical patent protection. Prior to this amendment, pharmaceutical products had been excluded from patentability. This article examines the patent application for the antiretroviral drug zidovudine, which was initially filed in 1986 with 15 claims covering the process for preparation of the pharmaceutical formulation. After the amendment to the Patent Act, the applicant attempted to amend the claims to protect the pharmaceutical formulation itself, but the new subject matter was denied, eventually leading to a Supreme Court decision in the matter.