This study assessed the efficacy of synthetic anticholinergic benztropine and incidence of side-effects in 20 developmentally-disabled patients with severe drooling. The double-blind, placebo-controlled, crossover protocol included one-week baseline, two-week placebo and two-week benztropine conditions (mean dose 3.8 mg). A significant decrease in drooling during the benztropine condition relative to placebo was demonstrated and conservative response rates (calculated by deleting placebo responders), ranged up to 65 to 70 per cent. For patients completing the protocol the incidence of side-effects did not differ across conditions and minor problems such as a dry mouth were eliminated by small dose adjustments. More serious cholinergic side-effects, which resolved within 24 to 48 hours, necessitated discontinuation of the drug in three patients. This study demonstrates that synthetic anticholinergics can provide an important therapeutic alternative to surgical and behavioral therapies for drooling.