Selenium-75 homocholic acid conjugated with taurine (75Se-HCAT) was used during loperamide administration in seven patients suspected of having bile acid malabsorption due to late radiation damage and small-bowel resection in order to document the aetiology of ileal dysfunction and to adjust therapeutic management. In two patients with ileal resection up to 50 cm and in one patient without resection, a reduction of bowel motility by loperamide resulted in marked normalization of the 75Se-HCAT retention measurements. Sequential scintigraphic 75Se-HCAT imaging demonstrated a significant improvement in the 75Se-HCAT reabsorption and recirculation, accompanied in one case by prolongation of colonic retention of the radiopharmaceutical. In four patients with more than 80 cm resection, the 75Se-HCAT test was abnormal during loperamide administration. In two of these patients for whom baseline values were available, no improvement in the pattern of 75Se-HCAT absorption was observed. In conclusion, the first results of loperamide 75Se-HCAT in patients suspected of having bile acid malabsorption and abnormal baseline 75Se-HCAT are promising. Intervention with loperamide is easy and seems to improve the clinical value of the test with direct therapeutic implications. Sequential 75Se-HCAT imaging is essential for interpreting changes in the 75Se-HCAT retention measurements.