GM-CSF is an important regulator of macrophage, granulocyte and dendritic cell behaviour and function. These cell types have been implicated in the retinal damage characteristic of endogenous posterior uveitis. Dendritic cells in the choroid have access to retinal antigens processed by the retinal pigment epithelial (RPE) cells of the blood-retinal barrier and are thought to be candidates for the presentation of antigen in uveoretinitis. We therefore investigated the production of GM-CSF and its regulation in human RPE cells. IL-1beta, tumour necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta (TGF-beta) all stimulated GM-CSF production by RPE cells and a combination of these cytokines increased GM-CSF production over five-fold compared with that with the individual cytokines alone. Interferon-gamma (IFN-gamma) rapidly down-regulated these responses. IFN-gamma did not appear to be acting directly on IL-1beta or via the synthesis of another protein. GM-CSF mRNA expression showed the same pattern of response to these cytokines, indicating transcriptional or pre-transcriptional regulation, and there was no evidence that IFN-gamma was acting by destabilizing GM-CSF mRNA. These results are generally important in understanding the ways in which cytokine regulation differs between different cell types and also more specifically for determining ways in which a cytokine with a significant role in the development of autoimmune uveoretinitis may be manipulated.