Iron deficiency has been reported in one third of patients with cystic fibrosis. There are data that suggest that iron absorption is increased with exocrine pancreatic deficiency and that administration of pancreatic enzymes may impair oral iron absorption. We compared oral iron absorption over a 3-hour period in the presence and absence of exogenous pancreatic enzymes in 13 stable young-adult patients with cystic fibrosis and 9 age-matched control patients. Although none of the patients with cystic fibrosis had a hemoglobin level less than 119 g/L, serum ferritin levels were less than 25 micrograms/L in 5 of the 13 patients, and the mean corpuscular volume was significantly lower in the patient group (86.1 +/- 2.7 vs 90.9 +/- 5 fL). Baseline mean serum iron levels were higher in controls (18.9 +/- 5.9 mumol/L) than in patients (11.9 +/- 6.3 mumol/L). There was no difference in iron absorption in the absence of exogenous pancreatic enzymes. Significant impairment of iron absorption was detected in both patients with cystic fibrosis and controls after administration of a preparation of pancreatic enzymes. There was an inverse relationship between iron stores, as measured by serum ferritin, and iron absorption. These findings suggest that long-term consumption of pancreatic enzymes by patients with cystic fibrosis may contribute to iron deficiency.