Our study was designed to investigate the production of interleukin-I (IL-I) and IL-6 in tumor-associated macrophages (TAM) isolated from ascites (I8 cases) or solid (7 cases) human ovarian carcinoma. These are pleiotropic monokines which, in addition to affecting proliferation and differentiation of lymphocytes, act on various targets, including vascular cells and liver, and may therefore be involved in the pathogenesis of certain manifestations of malignancy. IL-I was measured by the thymocyte co-stimulator assay, under conditions in which IL-6 was inactive, and, in 8 cases, by radioimmunoassay (RIA). IL-6 was measured as hybridoma growth factor (HGF) on the 7TDI cell line. TAM did not release appreciable levels of IL-l spontaneously and, upon LPS stimulation, were poor producers of this monokine compared to blood monocytes. In contrast, TAM supernatants contained a high level of HGF in the absence of deliberate stimulation, and exposure to LPS either did not affect or further augmented production of this monokine. HGF activity of TAM supernatants was completely blocked by anti-IL-6 antibodies. Ascites fluid from 8 ovarian-carcinoma patients contained high levels of HGF activity, blocked by anti-116 antibodies. Thus, TAM exhibit a dissociation in their capacity to release the functionally related monokines IL-l and 11-6. 11-6 produced by TAM may account for the elevation of liver-derived acute-phase proteins associated with malignancy.