The antisecretory (determined from salivary flow rates) and antimotility (determined from riboflavin absorption) effects of usually recommended doses of propantheline, hexocyclium, and isopropamide were compared in four adult volunteers. Both propantheline and hexocyclium significantly decreased salivary flow and increased riboflavin absorption. Although the usual dose of propantheline was about twice as effective as the usual dose of hexocyclium in suppressing salivary flow, these doses produced comparable effects on riboflavin absorption. Isopropamide had little or no effect on either the salivary flow rate or riboflavin absorption. Propantheline and hexocyclium elicited little effect on salivary flow when administered after a meal. Prolonged-release dosage forms of these drugs produced effects comparable to those produced by much smaller doses in conventional tablets and gave no indication of providing prolonged anticholinergic effects.