Mouse epidermal melanoblasts and melanocytes preferentially proliferated from disaggregated epidermal cell suspensions derived from newborn mouse skin in a serum-free melanocyte-proliferation medium (MDMD) and melanoblast-proliferation medium (MDMDF) supplemented with dibutyryl adenosine 3':5'-cyclic monophosphate (DBcAMP) and/or basic fibroblast growth factor (bFGF). Pure cultured primary melanoblasts and melanocytes were further cultured with MDMD/MDMDF supplemented with hepatocyte growth factor (HGF) from 14 days (keratinocyte depletion). The HGF increased the number of melanoblasts and melanocytes, but not the percentage of differentiated melanocytes in the melanoblast-melanocyte population in the absence of keratinocytes. Flow cytometry analysis showed that melanoblasts and melanocytes in the S and/or G2/M phases of the cell cycle were increased by the treatment with HGF. Moreover, an anti-HGF antibody supplemented to MDMD/MDMDF from the initiation of the primary culture (in the presence of keratinocytes) inhibited the proliferation of melanoblasts and melanocytes, but not the differentiation of melanocytes. These results suggest that HGF is a keratinocyte-derived factor involved in regulating the proliferation of epidermal melanoblasts and melanocytes from newborn mice in cooperation with cAMP elevators and/or bFGF.