We evaluated the validity of DNA enzymatic amplification (PCR) in a population at risk for HIV-1 infection, consisting of hemophiliacs and children born to seropositive mothers. All but one of the seropositive hemophiliacs and controls were found positive with the three sets of primers. All the seronegative patients and controls were found negative in PCR. No correlation with the anti-nef serology was found, one seropositive being anti-nef negative and three seronegative anti-nef positive. The results obtained with PCR are in good agreement with classical serology, and this would suggest that the possible period of latency may not be as long as suspected. No seroconversion has been described in hemophiliacs since solvent-detergent inactivated blood products have been in use, and seronegative hemophiliacs no longer constitute a population at risk. Studies on seronegative sexual partners of seropositive patients would be of great interest. For newborns from seropositive mothers, PCR is the only possible technique in early age before seronegativation of the healthy children. Further studies will be required to determine the fiability and sensitivity of the test.