Preliminary results from our laboratory with samples for HIV routine screening demonstrate repeatedly false reactive results in a frequency of 0.23% (27 false reactive of 11 527 sera tested with HIV Integral) and 0.28% (3 false reactive of 1056 sera tested with HIV DUO). With our standard third generation assay (HIV-1/HIV-2 third gener ation plus EIA, Abbott), we observed false reactive results in a frequency of 0.34% (390 false reactive of 113 045 tested sera). These results demonstrate that the prevalence of false reactiveresults is not increased with the fourth generation assays.