Twenty-one Caucasian patients (12 women and 9 men) were diagnosed as having lupus erythematosus tumidus by clinical and histopathological criteria. They were analysed by blood tests, histopathology and immunological studies and their response to treatment was recorded. While blood tests yielded non contributory results, histopathology showed in all cases a superficial and deep lymphocytic infiltrate with a perivascular and periadnexal involvement and an interstitial dermal deposition of mucin. Minimal epidermal changes were observed in 13 cases. In particular, epidermal atrophy was found in 8 specimens, hyperkeratosis in 8, parakeratosis in 2, acanthosis in 3 and spongiosis in 1. Four patients showed a slight vacuolar degeneration and periodic acid-Schiff staining showed a thickened basal membrane zone in two. Direct immunofluorescence was positive in 16 of the 19 patients tested. Antinuclear antibodies were negative in all 21 patients in indirect immunofluorescence. Antimalarials cleared the lesions within 12 weeks in 16 patients. Fourteen of them relapsed about 3 weeks after the first sun exposure, but were successfully controlled with the same treatment within a maximum of 12 weeks. Spontaneous resolution of the skin lesions was never observed. Altogether, some evidence of heterogeneity is suggested, some cases strictly satisfying Kuhn et al's criteria, others resembling discoid lupus more closely.