Hyperglycemia was induced with carbachol in rats, rabbits, and dogs, and the effect in rabbits was shown to be dose related. In albino rabbits with negligible plasma esterase activity, atropine sulfate effectively prevented hyperglycemia following 25 mcg./Kg. of carbachol, and the effect appeared to be dose dependent. In rabbits with moderate esterase levels, atropine sulfate dosage as high as 0.8 mg./Kg. had little inhibitory effect on carbachol hyperglycemic or cholinomimetic responses. This plasma esterase was not effectively blocked in vivo with 20 mg./Kg. of 2-(diethylamino)ethyl-2,2-diphenylvalerate (proadifen) HCl (SKF 525-A). However, this dose of proadifen HCl did block carbachol hyperglycemia in rabbits with negligible esterase activity. Carbachol hyperglycemia was similarly prevented by atropine in rats and dogs.