In 51 patients with acne vulgaris and 34 patients suffering from occupational oil acne the clinical effect of orally administered tetracycline was evaluated before, during and after a 3-monthly treatment (total dose of antibiotic: 1st month, 28.5 g; 2nd and 3rd months, 15.0 g). Patients treated with placebo were used as controls. Investigations of the skin fluorescence under Wood's light were performed during the treatment period. In one half of the patients with acne vulgaris and oil acne oral treatment with tetracycline had a very good clinical effect. The purpose of this investigation was the comparison of the results of the treatment of acne vulgaris and occupational oil acne with tetracycline.