We previously reported that mesenchymal cells (dermal fibroblasts and dermal papilla cells) can stimulate dopa oxidase activity in the skin melanocytes. This study extends the investigation of the influence of the fibroblast in a comparative study of melanogenesis in melanocytes from the hair, the skin and the eye. Culture of melanocytes with normal proliferative dermal fibroblasts slightly increased dopa oxidase activity of the hair, skin and ocular melanocytes (by 17, 11 and 28%, respectively), but co-culture with fibroblasts recovering from storage in liquid nitrogen or growth-arrested by means of gamma radiation showed much greater effects. Most dramatic results were obtained with fibroblasts, which had been both gamma-irradiated and then frozen in liquid nitrogen, where increases in dopa oxidase activity of 125, 227 and 185% for melanocytes of the hair, the skin and the eye, respectively, were seen. Experiments by using transwell cultures of melanocytes and fibroblasts and by using fibroblast-conditioned medium showed that a large proportion of this fibroblast influence could be mediated by diffusible factors, of which a good proportion was attributable to basic Fibroblast Growth Factor (bFGF). The addition of bFGF significantly increased dopa oxidase activity of the skin melanocytes, when fibroblasts were present, but not in their absence. These data show that fibroblasts in vitro, particularly when deliberately stressed, have the ability to increase dopa oxidase activity in melanocytes of the hair, the skin and the eye and further suggest that this effect is mediated by bFGF acting in combination with some other fibroblast-derived factors.