High levels of IL-6 have been observed in ascitic fluid in patients with ovarian cancer. In this study, we examined the effects of IL-6 on in vitro invasiveness of human ovarian cancer cells. Human ovarian cancer cells, NOM1 and SKOV, were used. Cell attachment to Matrigel, migration, and invasion were examined with or without IL-6. Zymography was performed to analyze gelatinase production by these cells. NOM1 cell attachment was increased by IL-6 (0 to 10 ng/ml). In a migration assay, IL-6 ranging from 0 to 10 ng/ml showed chemotactic and/or chemokinetic activities for the two cell lines. The invasiveness of these cells was significantly enhanced by IL-6 at the above concentrations. However, IL-6 did not modulate the production of either MMPs or TIMPs. IL-6 affects cell invasion through its effects on attachment and migration in human ovarian cancer cells. IL-6 might thus contribute to the progression of this disease.