Human immunodeficiency virus type 1 (HIV-1) can be isolated from lymphocytes and tissues of symptomatic and asymptomatic seropositive subjects. However, in some individuals, virus isolation is not always positive, especially in asymptomatics. In this paper we report the results of HIV-1 DNA detection by means of polymerase chain reaction (PCR), a new technique that permits the amplification of specific DNA sequences. PCR was carried out to amplify two highly conserved env regions on samples from 20 normal individuals used as controls, 20 seropositive patients at different stages of HIV disease and 25 seronegative individuals at high risk for infection, such as sexual partners of seropositive patients and intravenous drug addicts. Eighteen out of 20 seropositive subjects were positive by PCR while among seronegatives HIV DNA was detected in 7/25 individuals. Virus isolation was positive only in 2/7. These subjects, followed for HIV antibody production for a period of 10-12 months, remained seronegative except one case who seroconverted after a few weeks. Long latency of HIV infection without detectable antibodies seems prevalent in these subjects. PCR assay represents a useful technique for identifying proviral sequences in seronegative high-risk individuals, to confirm the infection during its early phases and during the follow-up of patients with HIV disease.