Rats were loaded with iron. With overload, up to a 10-fold increase of the iron and ferritin protein content of the livers was measured. The plasma ferritin concentration increased gradually with the ferritin concentration in the liver. The ferritin concentration in the bile increased also and was in the same range as in the plasma. The ratio plasma ferritin concentration to bile ferritin concentration in individual rats decreased in the case of considerable iron overload. After intravenous injection of liver ferritin, less than 2% of the ferritin concentration that disappeared from the blood was found to be in the bile. Isoelectric focussing revealed that the microheterogeneity of liver and bile ferritin were identical, but slightly different from plasma ferritin. These results indicate that ferritin was not solely leaking from the plasma to the bile. Together with ferritin, iron accumulated in the bile. The iron content of the bile ferritin was in the same range as in fully iron-loaded liver ferritin. It is likely that ferritin in the bile is excreted by the liver and consists of normal iron-loaded liver ferritin molecules. In all circumstances, the amount of iron in the bile was much higher than could be accounted for by transport by the bile ferritin. The ferritin protein to iron ratio in the bile was 0.1-1.2, which was in the same range as was measured in isolated lysosomal fractions of the liver. Those results agree with the supposition that ferritin and iron in the bile are excreted by the liver though lysosomal exocytosis.