Ferritins from normal adult human liver and heart were compared with ferritins from a lung carcinoma metastatic to liver and from HeLa cells on the basis of their isoferritin profiles, subunit composition, and immunological relationships. Each ferritin preparation gave different isoferritin profiles, but several contained common isoferritins. All of the tumor isoferritins had counterparts in the normal tissues. All ferritins contained similar subunits but in different proportions. Qualitative differences were demonstrable in some ferritins with antibodies to different tissue ferritins. These differences correlated with the subunit composition of the ferritins. By appropriate absorption, an antibody population was obtained that was apparently specific for one subunit type. Heart ferritin gave lines of apparent identity with the tumor ferritins with these antibodies. It is concluded that tumor ferritins are not tumor-specific antigens but correspond to isoferritins in normal adult heart.