Selenium (Se) status was evaluated in patients with intestinal failure requiring home parenteral nutrition (HPN). Ninety-two percent of patients (11 of 12) studied just prior to starting HPN had low serum Se values, and the mean value was 42 ng/ml, significantly less than mean values in disease controls with Crohn's disease not on HPN (76 ng/ml) and healthy controls (88 ng/ml). Eighty-five percent of patients (22 of 26) already on HPN for 2 to 109 months when studied had low serum Se levels (mean 38.4 ng/ml). The mean 24-hr urinary Se values were 3.7 micrograms in patients on HPN who did not have Crohn's disease, 10.9 micrograms in HPN patients with Crohn's, and 17.9 micrograms in healthy controls. In patients with Crohn's disease on HPN, a significant direct correlation existed between serum Se and the activity of whole blood glutathione peroxidase, a selenoprotein ; and a significant inverse correlation was found between serum Se and months of HPN. This study confirms that Se deficiency is very common in patients before starting and during HPN. These data and recent reports of cardiomyopathies associated with Se deficiencies in patients on HPN increase the importance of proper Se replacement and maintenance.