In earlier studies in this department, in which 0.5 g/day erythromycin (plus  topical benzoyl  peroxide)  was routinely given, it was demonstrated that risk factors exist. Younger patients  , males , patients with severe acne  and those with  truncal  acne   respond less well than older patients (i.e.  whose acne is now beginning to resolve naturally), females and subjects with less acne  and facial acne. Patients with a greater  seborrhoea  also  respond  less  well.