Summary.1 Iron in the form of ferric ammonium citrate was administered intravenously to rabbits in doses of 0.5–2.0 mg per kilogram of lwdy weight.2 The serum iron values observed within two minutes after the injection never exceeded 30 per cent of those calculated. In many cases they were materially lower than that. The following course of the serum iron curve showed a successive decline. After four hours the serum iron level still was above the initial fasting level.3 The “disappearance” of 70 to 80 per cent of the iron, already (luring the time of injection, is probably the result of a rapid distribution between the blood plasma and the extracellular tissue fluid. The following successive decline is probably explained by iron absorption of the tissue cells, to some extent perhaps also by excretion in the urine.4 The toxic signs following the injection of iron intravenously in relatively large doses are reported. The individual variations we