1. The ferritin content of iron-overloaded tissues was higher than that of normal tissues. There was also an increased iron content of ferritin extracted from these tissues.
2. In the limited number of tissues that we examined haemosiderin deposition appeared to be greater in the iron-overloaded livers than in the iron-overloaded spleens.
3. Ferritins extracted from iron-overloaded liver, spleen and kidney had similar properties to those extracted from the corresponding normal tissues.
4. Ferritin from iron-overloaded heart had a greater proportion of more basic isoferritins than had ferritin from normal heart.
5. Immunoreactivity to heart and spleen ferritin antibodies, subunit composition, iron content and rate of iron uptake of both unfractionated ferritin and isoferritin fractions separated by ion exchange chromatography were related to the isoelectric point.