Although the screening and supplementary tests for HIV antibody are very sensitive, they don't give direct evidence for the presence of virus. Also, antigen can precede the appearance of antibody, and some HIVinfected persons may be antigen positive but antibody negative at this early stage. The antigen detection method has also been used to assay for virus in cultures. In this study, we evaluated various commercial kits for sensitivity and specificity of HIV antigen detection in sera, plasmas, and cell culture specimens. Table 1 illustrates results on ten HIV antibody positive plasma specimens tested with Abbott Laboratories (Chicago, IL), Coulter Immunology (Hialeah, FL), and DuPont/Biotechnology Systems (Boston, MA) kits. Specimens #8 and #9 were positive only with the Coulter method and specimen #10 was positive only by DuPont. Table 2 shows the results of five antigen detection kits and the reverse transcriptase (RT) test for detection of HIV in cell culture specimens. All these specimens were eventually positive by both methods. Many of the tests were performed on culture fluids taken weekly on the same specimen, and the various kits were not always reacted with the same specimens. The DuPont and Abbott