The role of interleukin-1 (IL-1), a multifunctional cytokine which mediates important immune responses, was investigated in the growth of ovarian cancer cell lines in vitro. The messenger RNA for IL-1 alpha and IL-1 beta was expressed in six and four ovarian cancer cell lines, respectively out of eight. Measurement of IL-1 in the eight cell lines by enzyme-linked immunosorbent assay revealed that two lines, MCAS and TYK-nu, secreted a high amount of IL-1 alpha, but that none secreted IL-1 beta after 72 hours of incubation. The growth of these cells was significantly stimulated by the addition of recombinant IL-1 alpha (rIL-1 alpha) in a concentration-dependent manner in a 96 hour culture. The maximum response was obtained with 10 ng/ml of IL-1 alpha by counting the viable cell number using trypan blue. [3H]-thymidine incorporation by these cells was also stimulated by a 72 hour incubation with rIL-1 alpha. The spontaneous growth of these cells was inhibited by the addition of anti-IL-1 alpha antibody, anti-IL-1 receptor antibody or IL-1 receptor antagonist. These cells expressed two classes of IL-1 binding receptors on their surface as detected by [125I]-labeled rIL-1 alpha. These results indicate that IL-1 alpha is an autocrine growth stimulator for some ovarian cancer cells and suggest that IL-1 alpha plays an important role in the progression of this disease.