Regeneration of hemoglobin was studied in anemic rats fed a cereal-milk diet unfortified with iron or fortified with sodium iron pyrophosphate, reduced iron or ferrous sulfate. At the end of the 28-day period of iron repletion, mean body weight and mean concentration of hemoglobin were significantly greater for rats fed the diet fortified with ferrous sulfate than for rats in the other feeding groups. Rats fed the basal diet with no added iron (15 mg/kg of naturally occurring iron) had significantly lower hematocrits but not significantly different concentrations of hemoglobin than did the rats fed sodium iron pyrophosphate or reduced iron. Approximately 9% of the reduced iron, 10% of the sodium iron pyrophosphate, and 65% of the ferrous sulfate in the diet were incorporated into hemoglobin.