Bovine pituitary fibroblast growth factor (FGF) stimulates the incorporation of [3H]thymidine into DNA in serum-depleted cultures of some but not other human melanoma cells. The melanotic malignant melanoma cell line MIRW exhibited a 40% increase in [3H]thymidine incorporation into DNA and a 48% increase in cell number in response to 3.73 x 10(-9) M FGF. This same concentration of FGF produced a 22% increase in [3H]thymidine incorporation in the melanotic melanoma cell line Hs0294. However, FGF had no effect on the amelanotic melanoma cell line Hs0675, early-passage cultures of a human amelanotic melanoma (W-1), or early-passage cultures of a congenital nevus (N-1).