Pretreatment of normal male volunteers with the cholinergic muscarinic receptor-blocking drug pirenzepine (200 mg p.o.) abolishes the delayed GH response to a meal stimulus. In addition, the glycaemic and insulin responses to meals are significantly reduced following this dose of pirenzepine. The data suggest that the effect of pirenzepine on the glucose response to meals is at least partly independent of the inhibition of GH release. Our findings are of relevance to the further investigation of cholinergic muscarinic antagonist in diabetes mellitus.