We investigated the presence of the HIV-1 infection using the polymerase chain reaction (PCR) test in seronegative sexual partners of HIV-infected subjects and in children born to seropositive mothers. By using PCR assay, no HIV-1 DNA was detected in 32 female partners of HIV positive patients including three pregnant women who were also studied during pregnancy and after delivery. HIV-1 DNA was found in 12 out of 38 children born to seropositive mothers; five of them also had detectable serum HIV-1 p24 Ag levels. On the whole, our data stress the importance of using a very sensitive technique, i.e. PCR, for the early diagnosis of HIV-1 infection.