Four, 4-week old Friesian calves (BW=50±3 kg), fitted with duodenal, portal and jugular catheters and duodenal electrodes, were used to study the metabolism of duodenally infused betaine (Bet) or choline (Chol) and their effects on blood sulphur amino acids and duodenal myoelectrical migrating complexes (MMC). Animals were fed milk replacer at 5% BW twice daily, but were starved overnight prior to the experimental procedure. Animals received a saline infusion for 2 h at 1 ml/min followed by a 1 h infusion of 1·2 or 3·6 mmol of either Bet or Chol. Infusion of saline was continued for another 2 h after the cessation of the amino acid infusion. Duodenal MMC were measured with a computer-based data acquisition system (MacLab, ADI, Australia). There were no differences in measured blood metabolites between the jugular and portal vein; therefore, only average values were presented. Plasma Met concentrations increased from 20 μm, 20 min after initiating Bet infusion, whereas a lower dose of Chol decreased plasma Met and a higher one had no effect. The highest plasma methionine (Met) concentration (29 μm) occurred 45 min after the onset of the Bet infusion (1·2 mmol). Compared to the 3·6 mmol Bet infusion, the intraduodenal infusion of 1·2 mmol of Bet resulted in a greater area (P<0·001) under the plasma Met concentration curve (281·6 v. 73·3 mmol). A similar pattern was observed for plasma cystine concentrations. Infusion of Bet or Chol did not change the duration of MMC but Bet increased the number of spikes during the phase of low spiking activity (37·5 v. 14·6 pre-infusion, spikes/min; P<0·01). Chol had the same effect but only after the infusion ceased (29·3 v. 11·5 spikes/min; P<0·01). The velocity of migration of regular spiking activity (RSA; related to digesta transport) increased as a result of infusion (16·4 pre-infusion v. 31·3 Bet, 25·2 Chol cm/min; P<0·01). Chol caused an immediate increase in the velocity of migration of RSA, whereas with the Bet infusion an increase was observed after cessation of infusion. Increased concentrations of sulphur amino acids during Bet infusion could indicate that labile methyl groups may be limited in calves. Postruminal Bet and Chol supplementation may cause a decrease in nutrient absorption in the small intestine by increasing digesta transport.