Congenital hypomelanotic and hypermelanotic macules traced in three generations of a family suggested autosomal dominant inheritance. Some affected membbers also showed retarded growth and mental deficiency. Light microscopic findings of "splitdopa" preparations of lesional and normal skin were comparable, except that background staining of keratinocytes in dark macules was higher than in control skin. In light macules it was lower. Ultrastructurally, hypomelanotic skin showed small melanosomes (0.3 mu) that occurred in keratinocytes in melanosome complexes. Hypermelanotic skin revealed large melanosomes (0.6 mu) that were singly distributed in keratinocytes. Melanosome size in normal skin averaged 0.4 mu; distribution pattern was mixed. Melanin granules inside keratinocytes were fully melanized. Hyperpigmented, normal and hypopigmented skin of one person had histological features of black oriental and white skin. This clinical picture could well represent a new neurocutaneous syndrome different from tuberous sclerosis.