Smooth muscle involvement is relatively common in myotonic muscular dystrophy (MMD). The effects of cisapride on gallbladder motor function in myotonic patients have been investigated in 10 alithiasic patients and in 10 healthy volunteers. Gallbladder volumes were measured by ultrasonography in fasting state and 15, 30, 45 and 60 min after milk intake. The patients were treated with cisapride for two months, after which they underwent a second ultrasonographic examination. Gallbladder emptying was slower and less effective in dystrophic patients than in healthy volunteers. Cisapride was found to improve gallbladder kinetics (efficacy of contraction and rate of emptying) in patients affected with myotonic muscular dystrophy.