Serum levels of circulating oncostatin-M (OM) were compared among cases of Kaposi's sarcoma associated with acquired immune deficiency syndrome (AIDS-KS) and multiple controls, including a homosexual man infected with human immunodeficiency virus type 1 (HIV-1), an HIV-1-uninfected homosexual man, and a heterosexual man; and among classic KS cases and heterosexual controls. Cases were selected from abstracts collected by a population-based cancer registry and from local AIDS clinics. Controls for the AIDS-KS cases were matched to the cases by age, sex, and race and were either friends of the cases or residents from the cases' neighborhoods; controls for the classic KS cases were similarly matched, but were obtained solely from neighborhood residents. Blood samples were obtained from participants, serum levels of OM were determined by enzyme-linked immunosorbent assay (ELISA), and CD4 cell counts were obtained by flow cytometry. Geometric mean levels of OM were compared among the risk groups adjusted for age and CD4 cell count. No differences in adjusted OM levels were found between AIDS-KS cases and HIV-1-infected homosexual controls (8.4 pg/ml vs. 10.2) or between classic KS cases and controls (13.3 pg/ml vs. 9.6); however the HIV-1-infected controls (both homosexual and heterosexual) matched to the AIDS-KS cases had higher levels than did the HIV-1-infected cases and controls. Among the HIV-1-infected groups, an inverse correlation between OM and CD4 cell count was observed and was statistically significant for the cases. Among all heterosexual controls (matched to either case group), serum OM was inversely related to age.(ABSTRACT TRUNCATED AT 250 WORDS)