Using a clonogenic assay in vitro, it has been shown that exposure to azelaic acid (1-100 mM) for 24 hours has a dose-dependent effect on the survival of the colony-forming ability of murine (B16) and human (HMB2, and SK23) melanoma cells as compared with a non-melanotic non-tumoral Chinese hamster cell line (CHO). Both human cell lines were more sensitive to the diacid than the murine cells, and the HMB2 cells were more sensitive than the SK23 cells. These differences may be partly correlated with differences in pigmentation and doubling times between the three melanoma cell lines. The two human lines were more pigmented than the B16, and the SK23 more than the HMB2; the human lines had a longer doubling time than the others.