Host-tumor interactions in uveal melanoma are not well understood. It is believed that the cytokine interleukin-6 and the lipid mediator autacoid prostaglandin E2 are involved in tumor growth, proliferation, tumor cell survival, and angiogenesis. These cytokines have been shown to be poor prognostic markers in uveal and cutaneous melanoma. In this study, we investigated the levels of interleukin-6 and prostaglandin E2 in monocyte and uveal melanoma conditioned medium. Five human uveal melanoma cell lines (92.1, MKT-BR, OCM-1, SP6.5 and UW-1), and one monocyte cell line (28SC) were seeded in 6 well plates at a concentration of 1 x 10(6)cells ml(-1). After 18 hr melanoma conditioned medium was placed on the monocyte cell line and monocyte conditioned medium was placed on each uveal melanoma cell line. Tumor cells and monocytes incubated in fresh medium after 18 hr were used as controls. Interleukin-6 and prostaglandin E2 levels were determined by immunoassays prior to media transfer and 6, 12, 24, and 36 hr thereafter. In the absence of conditioned medium, neither product showed baseline levels of expression. Interleukin-6 but not prostaglandin E2, which remained undetectable for the duration of the study, showed up-regulation of expression after incubation in conditioned medium. 28SC incubated in melanoma conditioned medium expressed higher levels of interleukin-6 than did uveal melanoma cells incubated in monocyte conditioned medium. In addition each cell line exhibited a distinct pattern of expression with individual cell lines exhibiting peak levels of cytokine production at different time points. The results of this study offer insight into the mechanism by which interleukin 6 may be involved in tumor-host interactions potentially favoring tumor growth, survival, and proliferation.