75SeHCAT scanning was evaluated as a means of detecting bile acid malabsorption in patients with postvagotomy diarrhoea. Seven day 75SeHCAT retention ratios were measured in five patients with unequivocal post-vagotomy diarrhoea. The results were compared with an age matched group of asymptomatic control patients (n = 4) each of whom had previously undergone truncal vagotomy and drainage and a further group of normal volunteers (n = 6). The median 75SeHCAT retention ratios in patients with post-vagotomy diarrhoea was 2% (range 0-9%). In contrast, the median 75SeHCAT retention ratios in asymptomatic controls was 29% (range 26-61%) and 28% (range 19-70%) in normal volunteers. These results demonstrate that there is gross bile salt malabsorption in patients with post-vagotomy diarrhoea and that 75SeHCAT scanning is an effective screening test in these patients.