In Bantu subjects with iron overload iron is visible in skeletal muscle cells and in the tissue histiocytes which lie between these cells. In the present study the concentrations of `muscle' iron were measured chemically in subjects with varying hepatic storage iron concentrations. The results indicate that the concentrations of storage iron in `muscle' are much lower than those in the liver. However, the muscle mass is so large that the total amount of iron present is at least equal to that in the liver in subjects with normal body stores. The concentrations of iron in `muscle' are raised in subjects with iron overload but the degree to which they rise is far less than occurs in the liver; a thirtyfold increase in hepatic iron concentrations is associated with only a sixfold increase in `muscle' iron. Experiments in rats revealed that storage iron in `muscle' represents a relatively non-miscible pool which responds very little to acute changes in the iron environment.