Oxygen dissociation curves of crude haemolysates and of haemolysates purified through filtration by Sephadex of Triton cristatus raised at 4°C and 21°C were determined at the pH's of 6.4, 6.8, 7.0, 7.4, 8.0, at different temperatures. The results confirm previous findings that during acclimatation strong adaptive phenomena occur in the blood of the newts without any change of the molecule of haemoglobin. The adaptive phenomena are determined by the allosteric action of a small molecule on the haemoglobin. The nature of the molecule has not yet been determined: at present it seems rather unlikely that all the adaptive phenomena are mediated by the concentration of organic phosphates.