Delayed hypersensitivity reactions were investigated in 5 patients with febrile acne conglobata. Each of them had febrile periods, large abscesses and leukocytosis. They reacted negatively to tuberculin 10 TU/ml, to Schick toxin, to oidiomycin, to trichophytin as well as to 25 common contact allergens. DNCB did not induce sensitization in those 4 patients in whom it was carried out. However, the transforamtion of lymphocytes by phytohaemagglutinin (PHA) was normal. Five of 7 control patients with cystic or ordinary acne had positive tuberculin test reactions and 3 of them were sensitized to DNCB.