The effect of TGF-β2 on growth of uveal melanocytes in vitro was studied and the dose-dependent inhibitory effect of TGF-β2 was compared with the known concentration of TGF-β2 in aqueous humor. Uveal melanocytes were isolated and cultured with medium supplemented with cAMP elevating agents and basic fibroblast growth factor. The uveal melanocytes were plated into multi-well plates. After 24 hr, TGF-β2 was added to the medium in various concentrations. After 5 days, the cells were detached, counted and compared to the controls. The effect of TGF-β2 on DNA synthesis (as evaluated by uptake of bromodeoxyuridine) were also tested. TGF-β2 inhibited growth and DNA synthesis of cultured uveal melanocytes in a dose-dependent manner at concentrations from 0.03–10.0 ng ml−1. The growth-inhibition of TGF-β2was present even in serum-free medium. TGF-β2had little or no effect on melanogenesis of cultured uveal melanocytes. The serum used for cultivation did not contain active TGF-β1or TGF-β2as measured by immunoassay. The known amount of active TGF-β2 in aqueous humor (0.2–0.4 ng ml−1) is sufficient to inhibit the growth of uveal melanocytes. It indicates that TGF-β2 is a potent growth inhibit factor of uveal melanocytes and may play an important role in maintaining the non-proliferative, relatively quiescence status of uveal melanocytes in vivo.