We measured serum, blood, or red cell concentrations of various vitamins in 24 patients with Crohn's disease who had been free from any nutritional treatment, and compared them with those in 24 healthy controls. Twelve of the patients were affected in the small bowel only, two in the large bowel only, and the remaining 10 in both the small and large bowel. The fat-soluble vitamins A and E were significantly decreased in patients with Crohn's disease compared to controls. Among the water-soluble vitamins, vitamins B1, B2 and B6 and folic acid were more depleted in patients with Crohn's disease than in the controls, whereas vitamins B12 and C, nicotinic acid, and biotin were not different between the two groups, and pantothenic acid was increased in patients with Crohn's disease. In addition, vitamin B2 and nicotinic acid showed a negative correlation with the Crohn's disease activity index. These findings suggest that there is a variety of vitamin deficiencies in Crohn's disease prior to treatment and also that concentrations of some vitamins, such as vitamin B2 and nicotinic acid, may reflect the severity of the disease.