To determine whether concentrations of the anti-inflammatory peptide alpha-melanocyte stimulating hormone (alpha-MSH) are associated with accelerated or reduced disease progression in patients with HIV infection, plasma concentrations of alpha-MSH and two other anticytokine molecules, interleukin-1 receptor antagonist (IL-1 ra) and soluble tumor necrosis factor receptor (s TNF r), were taken repeatedly from HIV-positive patients over a 1-year period. Samples from 87 patients were collected by using special precautions to ensure accurate measurement of the peptide. Alpha-MSH concentrations were determined by radioimmunoassay; IL-1 ra and s TNF r concentrations were measured by using enzyme-linked immunosorbent assays. Clinical and immunologic variables were recorded to determine whether there is an association between cytokine antagonist concentrations and disease progression. Elevated concentrations of circulating alpha-MSH were associated with reduced progression of the disease. Circulating alpha-MSH was greater in non-progressors than in progressors; the association between elevated alpha-MSH and reduced disease progression was even more pronounced in patients with baseline CD4+ T cell counts less than 200/microL. No such association was observed for the other two anticytokine molecules, and there was no significant correlation between the plasma concentration of either cytokine antagonist and alpha-MSH. The present evidence and previous findings indicate that elevated concentrations of alpha-MSH are associated with reduced disease progression in HIV-infected patients.