During a herbal screening programme to find potential repigmenting agents for the treatment of vitiligo, Piper nigrum L. fruit (black pepper) extract was found to possess growth-stimulatory activity towards cultured melanocytes. Its aqueous extract at 0.1 mg/ml was observed to cause nearly 300% stimulation of the growth of a cultured mouse melanocyte line, melan-a, in 8 days (p < 0.01). Piperine (1-piperoylpiperidine), the main alkaloid from Piper nigrum fruit, also significantly stimulated melan-a cell growth. Both Piper nigrum extract and piperine induced morphological alterations in melan-a cells, with more and longer dendrites observed. The augmentation of growth by piperine was effectively inhibited by RO-31-8220, a selective protein kinase C (PKC) inhibitor, suggesting that PKC signalling is involved in its activity. This is the first full report on such an activity of black pepper and piperine.