In cell culture, azelaic acid (C9) has been shown to have an antiproliferative and cytotoxic effect on human and murine malignant cutaneous melanocytes. Normal melanocytes are unaffected, as are normal choroidal melanocytes. Here, effects on cell kinetics and ultrastructure of cells of a human choroidal melanoma line have been studied. Cells were exposed to single doses of disodium salts of azelaic (C(9)2Na) and adipic (C(6)2Na) acids at concentrations of 10(-2) M and 5 X 10(-2) M for 48 hr. C(9)2Na at 5 X 10(-2) M had a significant effect on proliferation at 24 and 48 hr and this was not reversible on removal of diacid. At 5 X 10(-2) M for 24 hr, C(6)2Na had no effect and at 5 X 10(-2) M for 48 hr had an effect which was marginally significant, but reversible. Swelling and disruption of mitochondria was seen in cells exposed to C(9)2Na at 5 X 10(-2) M for 1 hr and longer, but even at 10(-1) M, cells exposed to C(6)2Na were minimally affected. The results could encourage further investigations of the feasibility of azelaic acid therapy for uveal and ocular adnexal melanoma.