The Amplicor HIV-1 DNA PCR assay (Roche Diagnostics, Branchburg, NJ) requires 500 microl of whole blood for a diagnosis of human immunodeficiency virus type 1 (HIV-1) infection, and this amount is often difficult to obtain from infants. A comparison was performed using 100 and 500 microl of whole blood from infants less than 18 months of age. The concordance rate for HIV DNA PCR-negative and -positive samples was 100% for the two different volumes.