ObjectivesTo determine the amount of circulating CD4+ cells positive for intracellular p24 antigen during HIV infection, and to correlate the results with clinical, virological and therapeutic parameters.MethodsData were obtained from 24 anti-HIV-negative subjects (controls) and 47 anti-HIV-positive patients classified according to clinical diagnosis, serum p24-antigen assay results, and antiretroviral treatment with zidovudine, using a modified flow cytometric assay for the detection of intracellular HIV p24 antigen (p24-FCA) in circulating CD4+ lymphocytes.ResultsThe proportion of CD4+ lymphocytes positive for p24-FCA correlated well with HIV infection (1.685 ± 1.902 versus 0.160 ± 0.152 in controls;PPPConclusionsOur results suggest that CD4+ p24 Ag-FCA is a rapid and easy test for the identification of the proportion of CD4+ lymphocytes with intracellular p24 Ag, and that it could be more appropriate than serum p24 Ag assay in evaluating disease progression and efficacy of antiretroviral treatment.