SummaryThe effect of interferon-α (IFN-α) on virus replication in cells acutely infected with human immunodeficiency virus type 1 (HIV-1) and virus production from cells persistently infected with HIV-1 was studied. In both cell systems, significant suppression was observed. However, this suppression was not due to protein synthesis of the major viral proteins. Electron microscopy revealed the accumulation of intact virus particles on the cell surface of the cells treated with IFN-α. Thus, IFN-α might suppress the release stage of the particle from infected cells.