Gastric mucosal permeability to lithium has been measured in 20 patients with an untreated duodenal ulcer, eight patients who were asymptomatic for more than one year after truncal vagotomy and drainage, 14 patients with an endoscopically proven recurrent ulcer, and 21 patients with an unsatisfactory result from truncal vagotomy and drainage for other reasons. Lithium fluxes were lowest in the asymptomatic postoperative patients (0.149 +/- 0.028 mmol Li+/15 min), but were not significantly different to the measured fluxes in patients with a duodenal ulcer before treatment (0.160 +/- 0.020 mmol Li+/15 min) or a recurrent ulcer after truncal vagotomy and drainage (0.169 +/- 0.022 mmol Li+/15 min) (SEM). By comparison the mean lithium flux in patients who were dissatisfied with the results of their previous surgery for reasons other than a recurrent ulcer (0.234 +/- 0.019 mmol Li+/15 min) was significantly higher than that observed in patients with a duodenal ulcer (p less than 0.05), patients with a recurrent ulcer (p less than 0.05) or patients who were asymptomatic after definitive ulcer surgery (p less than 0.02). Furthermore, when the lithium fluxes observed in 11 patients whose major postoperative complaint was bile vomiting (0.243 +/- 0.027 mmol Li+/15 min) were compared with results from the remaining 52 patients included in the study (0.173 +/- 0.012 mmol Li+/15 min) fluxes were significantly higher in the 'bile vomiters' (p less than 0.05).