The purpose of this study was to establish norms for the serum ferritin determination. Analyses of blood samples submitted for a panel of 29 laboratory tests in 964,325 individuals of a random population of all races in 10 centers in the United States were used. A subgroup of 59,914 ferritin values was constituted from panels that showed the values of the 28 other laboratory tests inside prescribed limits that approached the conventionally used reference ranges. The selected group was taken to be more representative of normal ferritin values than the total group, because in the former group the accompanying 28 other test parameters approached normalcy. Although both groups showed a log-normal distribution of serum ferritin values, the values of the selected group were somewhat lower than those of the total population group. The percentile distribution for men and women of different ages is portrayed. In males, the median ferritin level increased from 23 micrograms/L at ages 12 through 16 years to reach a plateau in the 120s after age 32. Values in females remained in the 30s until menopause, after which values rose to about 80 micrograms/L. The validity of these data and their clinical significance are discussed.