The status of water- and fat-soluble vitamins was prospectively evaluated in 23 patients (13 men, 10 women, mean age 33 +/- 3 yr) admitted to the hospital with acute or subacute attacks of inflammatory bowel disease. Protein-energy status was also assessed by means of simultaneous measurement of triceps skinfold thickness, mid-arm muscle circumference, and serum albumin. Fifteen patients (group A) had extensive acute colitis (ulcerative or Crohn's colitis), and eight cases (group B) had small bowel or ileocecal Crohn's disease. Eighty-nine healthy subjects (36 men, 53 women, mean age 34 +/- 2 yr) acted as controls. In both groups of patients, the levels of biotin, folate, beta-carotene, and vitamins A, C, and B1 were significantly lower than in controls (p less than 0.01). Plasma levels of vitamin B12 were decreased only in group B (p less than 0.01), whereas riboflavin was lower in group A (p less than 0.01). The percentage of patients at risk of developing hypovitaminosis was 40% or higher for vitamin A, beta-carotene, folate, biotin, vitamin C, and thiamin in both groups of patients. Although some subjects had extremely low vitamin values, in no case were clinical symptoms of vitamin deficiency observed. Only a weak correlation was found between protein-energy nutritional parameters and vitamin values, probably due to the small size of the sample studied. The pathophysiological and clinical implications of the suboptimal vitamin status observed in acute inflammatory bowel disease are unknown. Further studies on long-term vitamin status and clinical outcome in these patients are necessary.