Hyaluronic acid (hyaluronate, HA) and type III procollagen N-terminal peptide were measured in jejunal perfusion fluid in an attempt to elucidate the turnover of connective tissue components in the small bowel in health and disease. In healthy controls (n = 16) the average concentration of hyaluronic acid in jejunal perfusion fluid was 12.2 +/- 2 micrograms/L (mean +/- SEM); the mean serum concentration was 22 +/- 7 micrograms/L. The type III procollagen N-terminal peptide concentration in jejunal fluid was 0.12 +/- 0.02 micrograms/L; the mean serum concentration was 12 +/- 0.7 micrograms/L. The albumin concentration in perfusion fluid was, on average, 0.04% of the serum values. Patients with celiac disease (n = 7) and Crohn's disease (n = 10) had normal serum levels of HA and type III procollagen N-terminal peptide. The jejunal secretion rate of HA was significantly increased in both disease groups and on average about three times higher than that in controls. The secretion rate of type III procollagen N-terminal peptide was not altered in celiac disease but increased more than three times in Crohn's disease. Habitual alcoholics investigated after alcohol withdrawal also had significantly increased jejunal secretion of HA but not of type III procollagen N-terminal peptide. In contrast, patients with alcoholic liver cirrhosis and similar ethanol intake had normal secretion of both substances. The findings of the study indicate that the secretion of HA into the jejunal lumen in health is considerable, possibly reflecting the rapid turnover of the intestinal mucosa. The enhanced jejunal secretion of HA in patients with celiac disease and Crohn's disease may be indicative of enhanced connective tissue response due to inflammation, but signs compatible with enhanced jejunal synthesis of type III collagen are only found in Crohn's disease. The HA secretion data in alcoholics might reflect (a) the active regeneration of the intestinal mucosa when ethanol is discontinued and (b) a possible role of the liver in this activity.