AIDS: Protease inhibitors (PRIs) are a diverse group of drugs which block an HIV-1 enzyme needed for the production of new viruses. PRIs stop the production of HIV in newly- or chronically-infected cells. There are currently six PRIs in clinical phase I or II trials: ritonavir, indinavir, Invirase, AG1343, U-103017, and VX 478; and there are four newly-identified PRIs soon to begin clinical trials: CGP 53 437, CGP 57 817, KNI-272, and A-80978. Eleven monotherapy studies of PRIs presented at the 35th Annual Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC) are described.