In order to determine the reference values of serum beta-carotene and its usefulness in the diagnosis of steatorrhea, 140 healthy subjects and 120 patients with suspected malabsorption syndrome were studied. The reference values, established in terms of the percentiles 2.5 and 97.5, were 85-270 micrograms/dL for men and 112-385 micrograms/dL for women. The beta-carotene diagnostic usefulness was determined by comparison with stool fat levels. According to ROC curves, steatorrhea was diagnosed at beta-carotene values of less than 89 micrograms/dL and 103 micrograms/dL for men and women respectively with a 78% sensitivity, 82% specificity, 76% positive and 84% negative predictive values and 80% accuracy. The steatorrhea prevalence (stool fat > 5 g/day) in our patients was 42%. Due to the implicit technical difficulties of the stool fat determinations and the results of this study, we propose the serum quantification of beta-carotene as an useful screening test in patients with chronic diarrhea and malabsorption syndromes.