RANTES has been found to suppress human immunodeficiency virus type 1 (HIV-1) replication. To further elucidate the role of this chemokine in HIV-1 infection, RANTES levels were analyzed in serum and platelet-free plasma (PFP) in 53 HIV-1-infected patients and 20 controls. RANTES levels were significantly elevated in both serum and PFP in all clinical stages of HIV-1 infection, with the highest levels in CDC groups A and B. In longitudinal testing, the progressors were characterized by a pronounced decline in serum levels over time; the nonprogressors, however, had only a slight reduction or an increase in RANTES levels. During 16 weeks of indinavir therapy, there was an increase in circulating RANTES levels and enhanced release of RANTES from stimulated CD8+ lymphocytes. The decline in RANTES levels along with disease progression is compatible with RANTES having a beneficial role in HIV-1-infected patients. The increase in RANTES levels during protease inhibitor-containing regimens may represent a previously unrecognized immunologic effect of such therapy.