In order to determine whether rokitamycin (RKM), one of the macrolide antibiotics, has any side effects on the gastrointestinal tract, the effect of intraduodenal administration of RKM (1.0, 3.0 and 9.0 mg/kg) on gastrointestinal contractile activity was studied by means of force transducers implanted chronically on the gastric body, gastric antrum, duodenum and upper jejunum in conscious dogs. Erythromycin (EM 0.3, 1.0 and 3.0 mg/kg) and kitasamycin (LM 1.0, 3.0 and 9.0 mg/kg), both macrolide antibiotics, were used as control drugs. RKM, when given at 3.0 mg/kg and 9.0 mg/kg doses, induced segmentation contractions only in the duodenum where it was administered. The duration of the RKM-induced contractions was 7.5 +/- 2.5 minutes for 3.0 mg/kg and 15.8 +/- 3.0 minutes for 9.0 mg/kg, and the contractile force of the contractions was 43 to 82% of the maximum contractile force of the interdigestive contractions in the duodenum. EM, at 0.3 mg/kg, evoked a series of strong contractions quite different from those induced by RKM but similar to the natural interdigestive contractions, and with large doses, dose-dependent long-lasting interdigestive contractions were induced. On the other hand, LM did not stimulate notable gastrointestinal contractile activity even at a 9.0 mg/kg dose. In order to eliminate the possibilities of the contraction being caused by the effect of RKM on the duodenum through the general circulation upon absorption, 3.0 mg/kg RKM was given intravenously. It was found that intravenous injection of RKM did not evoke any contractions attributable to the direct action of RKM in the circulation.(ABSTRACT TRUNCATED AT 250 WORDS)