Eighteen asymptomatic men with persistent human immunodeficiency virus type 1 (HIV-1) p24 antigenemia were treated with zidovudine 250-500 mg (+/- acyclovir 800 mg) 6-hourly for 4-12 weeks, and thereafter with zidovudine 500 mg (+/- acyclovir 1600 mg) 12-hourly for 92 weeks. Six additional HIV-1 p24 antigenemic subjects were treated with zidovudine 500 mg 12-hourly for 76 weeks. Disease progression occurred in 4 subjects, despite sustained reduction of serum HIV-1 p24 antigen levels: Pneumocystis carinii pneumonia was diagnosed after 60, 80, 90 and 93 weeks, respectively. The median CD4+ cell count of these 4 men at study entry was 0.2 x 10(9)/l, and it declined to 0.07 x 10(9)/l at the moment AIDS was diagnosed. In 20 subjects no disease progression occurred. The median CD4+ cell count of these 20 men at study entry was 0.4 x 10(9)/l and it was 0.45 x 10(9)/l at the end of the study period. Median serum HIV-1 p24 antigen levels at the end of the study period were 42% lower than at study entry in these 20 subjects. In 5/20 men, an initial decline was followed by a rise in antigen levels to above pretreatment value. Treatment with zidovudine was well tolerated. Anemia caused symptoms in 3/24 men, but prolonged leucopenia or neutropenia did not occur. None developed clinical or convincing biochemical evidence of zidovudine-associated myopathy.