In a group of 56 patients being evaluated for iron storage disease, all of whom underwent liver biopsy with quantitative measurement of liver iron concentration, urinary excretion of iron was measured following intramuscular injection of deferoxamine (10 mg/kg body weight). Urine was collected in two portions, 0-4 h and 4-24 h after deferoxamine administration. Iron excretion in the first 4 h was closely correlated to that over the entire 24-h period (r = 0.88, p less than 0.0001, 95% confidence interval = 0.80-0.93), indicating that the 4-h deferoxamine urinary excretion test can be adapted readily to an outpatient clinical setting, helping to insure complete and accurate urine collections. Correlation of 0- to 4-h urinary iron excretion and quantitative liver iron (r = 0.335), although higher than for the full 24 h (r = 0.192), was not sufficient to accurately predict hepatic iron concentration in the individual patient.