We evaluated a less-sensitive enzyme immunoassay (3A11-LS) for its possible use for early diagnosis of human immunodeficiency virus type 1 (HIV-1) infection in infants. The results were compared with those from the immunoglobulin G-capture enzyme immunoassay. A total of 239 sera from 77 infants were tested. All 25 sera from the 10 infants born to seronegative mothers were found to be negative by both assays. Forty-one seroreverting infants showed a complete decay of maternal antibodies by 4 months by the 3A11-LS assay. However, the assay detected HIV antibodies in only 9 (36%) of 25 sera collected from infected infants between 4 and 6 months and in 27 (63%) of 43 sera collected after 6 months of age. Further analysis with alternative cutoff values indicated that the 3A11-LS had a sensitivity of 12 to 44% and a specificity of 90 to 100% for infants between 4-6 months of age. This data suggest that a diagnosis of HIV infection in some of the infants could be made after 4 months of age by the 3A11-LS assay, although a negative 3A11-LS test result may not rule out infection and may require a further followup.