Two patients with AIDS are described who developed acral hyperpigmented macules of the fingers, palms and soles, buccal mucosa and genitalia, associated with longitudinal melanonychia. These pigmentary changes seemed to be independent of zidovudine and were associated in one with diffuse melanoderma and elevated levels of alpha-MSH. Histological and ultrastructural studies showed an increase of the dendrites and pigmentation of the melanocytes and few melanosomes in the keratinocytes.