OBJECTIVE - Because muscarinic cholinergic agonism in the absence of an increase in glucagon secretion inhibits hepatic glucose production, we tested the hypothesis that muscarinic cholinergic antagonism enhances glucose recovery from hypoglycemia in insulin dependent diabetes mellitus (IDDM). RESEARCH DESIGN AND METHODS - Eight (initially euglycemic) patients with IDDM received overnight infusions of insulin and were studied on three occasions in random order Hypoglycemia was induced by low-dose insulin infusion (4.0 pmol · kg-1 · min-1) from 0 through 80 min; observations were continued through 240 min. At 0 and 80 min, intravenous injections of atropine only (1.0 mg), placebo and then atropine, respectively, or placebo only were administered. RESULTS - Increments in heart rate (P < 0.001) and prevention of the pancreatic polypeptide response to hypoglycemia (P = 0.042) after atropine administration documented muscarinic cholinergic antagonism. The absent glucagon response to hypoglycemia was unaltered, but the epinephrine response was increased (P = 0.010). Nonetheless, rates of glucose production and utilization and plasma glucose concentrations were unaltered. CONCLUSIONS - We conclude that muscarinic cholinergic antagonism does not enhance glucose recovery from hypoglycemia in patients with IDDM.