This guideline describes the preclinical documentation required for a new drug active against human immunodeficiency virus (HIV) and offers suggestions regarding the design and implementation of phase 1, 2, and 3 clinical trials. Drugs with a low level of potential toxicity, especially those that are not nucleoside analogues, should be evaluated in healthy individuals who are not infected with HIV before trials in HIV-infected patients commence. The guideline also discusses possible clinical and laboratory end points for efficacy and emphasizes the need for careful validation of all laboratory end points used. The approach of the guideline is deliberately general: more specific recommendations would soon become outdated in this field, which is characterized by extremely rapid developments. © 1993 by The University of Chicago.