The albinotic skin and hair of 2 patients with Hermansky-Pudlak syndrome were investigated by light and electron microscopy. Incubation of hairbulbs and epidermis in 1-dopa revealed a weak tyrosinase activity. The epidermal melanocyte population was of normal density. The most striking feature was the presence of numerous giant melanosomes resembling those mainly reported in various hyperpigmented skin lesions. The association of this melanosomal disorder with the platelet dysfunction and ceroid storage typical of the autosomal recessive Hermansky-Pudlak syndrome might provide new insights into the mechanism leading to formation of giant melanosomes.