It has been shown that the two successive C′ reaction steps requiring Ca++ and Mg++, respectively, are followed by a third process which we have termed the terminal intrinsic transformation reaction, in the course of which intact cells release their hemoglobin and become ghosts. The terminal reaction proceeds at an appreciable rate even at 0°C. It is not influenced by changes in ionic strength, or reaction volume, nor do citrate or EDTA in moderate concentration have any effect.