THE low toxicity of iron-dextran complex ('Imferon') has made it possible to follow for the past eighteen months the effects of administering intramuscularly a total dose of 1,650 mgm. iron per kgm. to rats. Control animals on the same diet (M.R.C. diet 41 containing 1 per cent of cod liver oil) over the same time were treated with equivalent amounts of dextran, without iron.