CD4-dependent HIV envelope glycoprotein-induced membrane fusion events play a key role in the life cycle of HIV and are involved both in infection mediated by viral particles and in virally mediated cytopathic processes. The relevant events involve binding interactions between the HIV envelope glycoprotein gp120 and the cellular receptor CD4 and membrane fusion processes mediated by the HIV envelope glycoprotein gp41. A straight forward, rapid, and convenient assay procedure useful for analysis of these processes and identification of inhibitors is described. © 1993, Elsevier Inc. All rights reserved.