Twenty-seven of 66 patients with Crohn's disease had reduced concentrations of selenium and glutathione peroxidase in plasma and erythrocytes. When the patients were subgrouped according to the length of resected small bowel, a significant reduction of selenium and glutathione peroxidase in both plasma and erythrocytes was only found in patients with a resection > 200 cm. A highly significant correlation between selenium and glutathione peroxidase was found in plasma (r = 0.81) as well as in erythrocytes (r = 0.62), but no correlation was observed in the control group. A statistically significant correlation was also found between plasma selenium and the Harvey-Bradshaw score (r = -0.44), body mass index (wt/ht2) (r = 0.47), and plasma albumin (r = 0.29). Patients with a small-bowel resection > 200 cm appear to be at risk of developing severe selenium deficiency. These patients should have their selenium status monitored and probably receive selenium supplementation.