Serum levels of IL-8 were determined in HIV-infected individuals and the results were compared with those for HIV- controls. The IL-8 levels were measured by an ELISA with a MoAb and a polyclonal antibody to recombinant IL-8. The means and 95% confidence intervals of IL-8 in sera of 36 HIV-infected individuals and 32 matched controls were 275 and 216-349 pg/ml, and 8 and 4-14 pg/ml, respectively, showing a 34-fold increase in IL-8 in the circulation of HIV-infected individuals. This increase does not appear to be related to the disease state, infection or systemic medical agents. This finding suggests the possible involvement of IL-8 in the pathogenesis of HIV-induced disease.