The effect of human immunodeficiency virus type 1 (HIV) infection on semen parameters that assess fertility was investigated in 50 semen specimens from 21 asymptomatic or minimally symptomatic HIV-seropositive men and 3 specimens from 3 men with AIDS. HIV was isolated from 15 (30%) of 50 specimens from asymptomatic or minimally symptomatic persons and from 1 of 3 specimens from patients with AIDS. The men with AIDS all had pyosemia and grossly abnormal sperm. In contrast, semen specimens from other seropositive men did not differ significantly from semen specimens from healthy seronegative semen donors. No abnormality in sperm count, morphology, numbers or types of leukocytes in semen, or other seminal parameters was associated with HIV shedding in semen. Zidovudine therapy did not affect sperm morphology or seminal characteristics. Thus, although patients with AIDS had abnormal semen, the laboratory parameters that assess fertility were not affected by shedding of HIV in semen or concomitant therapy with zidovudine.