Although human immunodeficiency virus type 1 (HIV-1) has been found in numerous body fluids, there are no reports of attempts to demonstrate this virus in eccrine sweat, a fluid frequently encountered during person-to-person interactions. "Natural" eccrine sweat samples and blood from 50 HIV-1-seropositive patients and 2 HIV-1-seronegative controls were cultured for HIV-1 by a cocultivation method. Polymerase chain reaction for HIV-1 RNA and proviral DNA was done on 40 sweat samples (39 patients, 1 control). HIV-1 was isolated from peripheral blood mononuclear cells of 39 (78%) of 50 patients but from none of 52 sweat samples. No HIV-1 viral DNA or RNA was detected in the 40 sweat samples tested. With present methodology, infectious HIV-1 cannot be demonstrated in "natural" eccrine sweat samples from HIV-infected patients.