A double-blind, randomized multi-centre study was performed to evaluate the efficacy of a 4% erythromycin and zinc combination (Zineryt) versus 2% erythromycin (Eryderm). One-hundred and twenty-two patients suffering from acne vulgaris were treated with either Zineryt lotion or 2% erythromycin lotion. Acne grading and lesion counts for comedones, papules, pustules, nodules and macules were performed at each visit at 0, 1, 2, 4, 8 and 12 weeks. Treatment with Zineryt lotion was found to be more effective than with 2% erythromycin as regards the reduction in number of the acne lesions and the severity grade of the acne.