Because exposure to semen is important for the sexual transmission of human immunodeficiency virus type 1 (HIV), the relationship of stage of infection and antiviral chemotherapy to isolation of HIV from semen was investigated. Whereas HIV was isolated from peripheral blood mononuclear cells of all seropositive persons tested, it was isolated from semen in only 11 (32%) of 34 men, including 3 of 6 who were studied sequentially over time. HIV was isolated from 6 (32%) of 19 semen specimens from 14 asymptomatic persons (Centers for Disease Control [CDC] class II or III) and from 10 (28%) of 36 semen specimens from 20 symptomatic patients (CDC class IV). Isolation of HIV from semen did not correlate with CD4+ or CD8+ T lymphocytes counts or zidovudine therapy. Seropositive men may shed HIV in semen early in the course of infection, and zidovudine therapy seems to have no effect on the recovery of HIV and, thus, on the potential for sexual transmission of HIV.