To promote progress in the research and development of early diagnostic tests for HIV in young children an international workshop was held on January 17-18, 1992, in Siena, Italy. Experts on pediatric AIDS, diagnostic retrovirology, and immunodiagnosis discussed and summarized the state-of-the-art and made recommendations for general application of several tests and further evaluation and continued research for other candidate tests. From the discussions it was clear that the field has advanced beyond the time when it was necessary to wait until the infant reached 18 months of age before attempting the diagnosis with conventional serologic tests for HIV. About half of infected infants can now be identified at birth, approximately 90% by 3 months of age, and almost all by 6 months of age using HIV culture and polymerase chain reaction assays. IgA antibody tests and p24 antigen tests have also proved useful, although they are not as sensitive in newborn infants. The fact that HIV can be detected in only one-half of infected infants at the time of birth points to the need for further research on the timing of transmission and the natural history of perinatally acquired HIV infection to understand the limitations of current early diagnostic tests and to develop new approaches to overcome these problems.