AbstractWe have studied the haemolysing action of lysocithin on the chromocytes of man, rabbit and sheep. It was found that the amount of lysocithin needed to haemolyse a red cell is sufficient to cover this cell by a monomolecular layer. In view of the fact that lysocithin alters the shape (and therefore the surface) of the chromocytes before haemolysis sets in, no very accurate check is possible.The lysocithin used was prepared from egg‐yolk. In a series of preliminary experiments with lyosocithin prepared from ovolecithin Merck the general features of lysocithin haemolysis were studied. It was shown that the number of chromocytes haemolysed by a given quantity of lysocithin is independent of the concentrations used. And further, that the process of lysocithin haemolysis is terminated within less than 15 minutes, even if insufficient lysocithin is present for the haemolysis to be complet