The blocking effects of aspirin, chlorpheniramine, and cimetidine were tested against the flush provoked by alcohol in twenty-four chlorpropamide-treated patients with non-insulin-dependent diabetes mellitus. Active preparations were compared in a double-blind manner with an indistinguishable placebo. Aspirin significantly decreased the number of patients who flushed. Five patients studied in detail all showed suppression of chlorpropamide/alcohol flush by aspirin, with a mean facial temperature increase during the flush of 2.4 degrees C after pretreatment with placebo and an increase of 0.4 degrees C after pretreatment with aspirin.