Serum retinol and serum carotene concentrations were determined over a 6-month period in 137 outpatients with Crohn's disease. Serum retinol measurements were within the reference range for all patients at each assessment period, while serum carotene levels were low in about one quarter of the patients. Of the 56 patients who completed 48-hour stool collections, 41% had stool fat values exceeding the reference value. Serum retinol concentrations were not significantly correlated with the serum carotene concentrations, with the 48-hour stool fat content, or with the Crohn's disease activity. In contrast serum retinol concentrations were correlated with the dietary levels of vitamin A. Serum carotene concentrations were inversely correlated with the stool fat content but were not related to Crohn's disease activity or dietary levels of carotene or total vitamin A. Thus: (1) serum retinol concentrations were normal in this moderately large group of patients with Crohn's disease and did not reflect a low dietary vitamin A intake by 34% of the population; (2) serum carotene levels were frequently low in patients with Crohn's disease, possibly due to the presence of steatorrhea, but were not related to low dietary intakes of carotene or to active Crohn's disease, and (3) a low serum level of carotene does not indicate that the patient is at risk of developing vitamin A deficiency.