The elevation of serum iron level was noted in six out of 45 patients with breast cancers who were treated by medroxyprogesterone acetate (MPA) in Kinki University Hospital. Those six patients were not found to be involved in hemolysis and liver dysfunction during the treatment. The level of serum iron was demonstrated 205-338 micrograms/dl in the blood after MPA treatment. This elevation of serum iron level was not related with another anti-cancer agents. There was no observed serious complication with high level of serum iron. This is the first report of the elevation of serum iron level following MPA therapy for the patients with breast cancers.