The effects of the antidopaminergic drug sulpiride on gastric acid secretion and gastrin release have been evaluated in 42 healthy individuals. Basal and submaximal pentagastrin (0.5 micrograms/kg-h)-stimulated gastric acid secretion, as well as basal and meal-induced gastrin secretion, were studied after acute intramuscular administration of racemic sulpiride (100 mg) and its L-(50 mg) D-(50 mg) isomers. Racemic and L-sulpiride significantly decreased stimulated serum gastrin concentration, but they did not affect fasting serum gastrin or basal and stimulated gastric acidity. D-sulpiride significantly decreased gastric acid secretion, without affecting serum gastrin levels. While the effects of racemic and L-sulpiride are analogous to those of other antidopaminergic drugs, D-sulpiride mimics the action of dopamine, at least at gastric level. These data support the hypothesis that the D-isomer may possess agonist-antagonist activity at dopamine receptors. Since racemic sulpiride has been used with conflicting results in the therapy of patients with peptic ulcer, in the light of the present results it would be of interest to study separately the efficiency of the D- and L-isomers of the drug in healing peptic ulcer.