Several serological techniques may be used for the detection of HIV infection, however, in the case of infants, there are no methods that are effective prior to the loss of maternal antibodies. Thus, in such cases, a completed series of serological and virological assay of HIV antibodies should be performed in follow-up studies. Twenty children living in Modena (Italy) were studied since 1985. Seven of these children were of ages ranging from 3 to 10 years. Only one of them was found to be seropositive for HIV. The remaining 13 children were studied from birth. Six had lost maternal antibodies to HIV at a median age of 15.1 months. Four showed decreasing levels of the anti-body by Western blotting. HIV antigen was detected in serum samples from 2 children. The data reported stress the need for longitudinal studies that could lead to reliable methods of diagnosing HIV infections in newborns.