Abstract: The skin biopsy specimens from fifteen patients with Langerhans cell histiocytosis were studied. Thirteen out of fifteen cases were positive to S100 protein antibody and peanut agglutinin, but negative to Mac387 and lysozyme antibodies, and three cases were positive for CD₁ antibody by immunohistochemistry. Birbeck granules were demonstrated in one of the three cases by electron microscopy. Ten cases were analysed by flow cytometry, six cases (60%) were aneuploid, DNA index was 1.38±0.32, proliferative index was 38.69%. These results showed that these pathognomonic histiocytes were of Langerhans cell origin and their potential malignancy could not be ruled out.

Key words: Histiocytosis X