Skin biopsies from nine patients with a histological and/or clinical diagnosis of cutaneous lymphocytoma, lymphoplasia or Jessner's lymphocytic infiltrate were examined by immunoenzymatic labelling with a panel of monoclonal antibodies against lymphocytes and accessory cells. Similar cellular constituents were demonstrated in the biopsies from three patients with lymphocytoma, two with lymphoplasia and two with atypical lymphocytes, but a protracted benign clinical course. The infiltrates from these patients consisted of T cells, Langerhans cells, related HLA-DR positive dendritic dermal cells and clusters of polyclonal B cells. In four patients, the B cell clusters contained B cell accessory follicular dendritic cells, and thereby closely resembled the B cell follicles seen in lymphoid organs. The T cells were predominantly T helper/inducer cells and in all patients the T cells expressed HLA-DR. One patient diagnosed as lymphocytoma cutis differed from the other patients by having no detectable B cells. One patient with Jessner's lymphocytic infiltrate differed from the other patients by having a marked relative predominance of T suppressor/cytotoxic cells. These data suggest that cutaneous lymphocytoma and lymphoplasia are basically similar disorders which may be considered to be exaggerated immune responses, whereas Jessner's lymphocytic infiltrate may be a separate entity. Immunological analysis may assist in establishing a definite diagnosis in cases of lymphocytoma or lymphoplasia with atypical cytological features.