Plasma erythropoietin values were determined in 1122 hospitalized and outpatient children aged 1 to 18 years with a commercially available enzyme-linked immunosorbent assay. A computerized approach based on the Hoffman technique was used to establish erythropoietin reference ranges. Plasma erythropoietin values ranged from 1.0 to 21.9 mIU/ml in male subjects, and from 1.1 to 20.5 mIU/ml in female subjects (2.5th to 97.5th percentiles).