In order to assess ileal dysfunction in patients with complaints after pelvic radiation therapy, retention measurements and scintigraphic imaging with selenium 75 homocholic acid conjugated with taurine (75Se-HCAT), combined with the carbon 14 glycochol breath test, were evaluated in 39 patients. In 22 patients without ileal resection the results of the 75Se-HCAT test and the breath test differentiated between a normal functioning ileum (both tests negative) and ileal dysfunction as a cause of complaints (one or both tests positive). Among the patients with ileal dysfunction, the combination of both tests permitted those with bacterial overgrowth (breath test positive, 75Se-HCAT negative) to be separated from patients with evidence of bile acid malabsorption (75Se-HCAT positive, breath test positive or negative). In 17 patients with small-bowel resection, the 75Se-HCAT test helped to estimate the severity of bile acid malabsorption with implications for therapy. In this group the breath test was false-negative in 7 cases with abnormal 75Se-HCAT. Additional systematically performed scintigraphic imaging improved the accuracy of the 75Se-HCAT test, revealing cases with prolonged colonic accumulation of the radiopharmaceutical, causing spurious retention values. In conclusion, assessment of ileal dysfunction by nuclear medicine techniques in post-irradiation conditions provides information about the aetiology and therefore the possibility of adjustment in the clinical management.