The 1-(14C)-glycine-glycocholic-acid breath test was evaluated in 10 normal subjects and in 38 patients with Crohn's disease. Twelve patients were non-operated and 26 had been subjected to ileal resection (10-180 cm). In addition, coecal resection or right-sided hemicolectomy was performed on 20 patients and subtotal colectomy on six. The 14C-excretion in breath was abnormally elevated in only 16 of the 38 patients with Crohn's disease. Combining 14C-excretion in both breath and faeces, the test was found to be correlated with the activity of the disease in non-operated cases, whereas all resected patients were found to have bile acid malabsorption. It is concluded that the breath test is useless in Crohn's disease without concomitant measurement of the radioactivity in stools. The faecal 14C-excretion was correlated with the extent of ileal resection and with the extent of colonic resection, whereas the 14C-excretion in breath was independent of the type of operation performed. The breath test was found to be a more sensitive assay for ileal dysfunction than the duodenal bile acid concentration and the vitamin B12 absorption. No correlation with an elevated G/T-ratio and an abnormal bacterial growth was found.