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The authors studied by histoenzymology and electron microscopy, repigmentation induced by oral photochemotherapy (8-MOP-UVA) in 4 patients with vitiligo. The presence of hypertrophic melanocytes was demonstrated in the middle and deep portions of certain centre of islands of repigmentation. Melanocytes comparable to these were also observed in the epidermis of the peripheral collerette in the island of repigmentation. No melanocytic mitosis could be seen in the repigmenting epidermis. Ultrastructural study showed that the melanocytes of the repigmented zones were hyperactive. The melanosomes which they synthesize have a slightly larger size than the melanosomes of the neighbouring healthy skin. Their mode of intrakeratinocyte grouping was not altered. These results suggest that the origin of the melanocytes which repigment the vitiliginous epidermis under the influence of PUVA derives probably from a melanocytic reservoir localized in the hair follicle.