The presence of the human immunodeficiency virus type 1 (HIV) provirus was assessed in peripheral blood mononuclear cells (PBMCs) from 27 offspring of HIV-infected mothers, 12 of these mothers, and 4 HIV-uninfected mother-infant control pairs. Enzymatic amplification of specific conserved regions of the gag and env genes was performed directly in PBMC lysates using the polymerase chain reaction (PCR) technique. The enzymatically amplified gene products were evaluated using the oligomer hybridization detection procedure. PBMCs from infected infants (as determined by Centers for Disease Control clinical criteria) and from HIV-infected mothers manifested a characteristic HIV oligomer hybridization product. Clinically uninfected seropositive infants with declining HIV antibody titers and infants who became seronegative lacked an enzymatically amplified HIV gene product. These preliminary data indicate that PCR is a valuable diagnostic technique to detect or exclude HIV infection in young infants and children.