Some authors have suggested that Langerhans cells (LCs) are present in the dermal infiltrate of skin lesions from patients with mycosis fungoides (MF). They base their findings on the presence of T6-positive cells [1, 5, 7, 8, 13] or ultrastructural recognition of Birbeck granules, which are considered specific cytological markers of LCs [6, 14]. However, also dendritic cells closely resembling the interdigitating reticulum cells (IRCs) described by Veldman  in secondary lymphoid organs have been recognized ultrastructurally in the dermal infiltrate of MF [2, 3] and IRCs too have been reported to be able to express T6 antigens . Moreover, in another cutaneous T-cell lymphoma, i.e., Srzary syndrome, a disease closely related to MF, numerous dendritic cells quite similar to IRCs have been found but not LCs . Because of these conflicting reports we performed an immunohistochemical and ultrastructural study on 10 skin lesions at various clinical stages (i. e., patches, placques, and nodules) from 7 patients with MF, with the aim of establishing the nature of the accessory cells in the dermal infiltrate. Our ultrastructural examination, performed on numerous ultrathin sections cut at various levels in each specimen, invariably revealed the presence in the dermis of numerous dendritic cells with the features of IRCs, which were devoid of Birbeck granules and in close apposition with mycosic cells (MCs) (Fig. 1). Only in a specimen taken from a very early patch did we find a single LC in the dermis and without an MC nearby (Fig. 2).