In an open-label dose-ranging pilot trial, 13 homosexual men with human immunodeficiency virus type 1 (HIV-1) p24 antigenemia after at least 6 weeks of zidovudine monotherapy were continued on zidovudine and given interferon-alpha, 1.25-7.5 x 10(6) units/m2 subcutaneously three times/week. Plasma p24 antigen levels demonstrated a biphasic response, falling initially in 11 patients by a mean of 50% (95% confidence interval, 36%-64%; P = .001) at a median of 11 weeks, but rising steadily thereafter (P = .001). CD4+ cell counts fell by a mean of 7.1 cells/mm3/week (P = .01). Higher initial CD4+ counts predicted greater p24 antigen reductions. At higher interferon doses no greater reductions in p24 antigen occurred, but side effects were more severe and CD4+ lymphocyte counts fell faster. Polymerase chain reaction quantification of HIV-1 DNA in 3 patients showed a biphasic pattern paralleling the p24 antigen response. In sum, although evidence of short-term effects was found, the combination showed no evidence of lasting antiviral activity beyond that achieved with zidovudine alone in patients with advanced HIV-1 infection.