The rates of rise of the plasma potassium concentrations are not affected by the nature ot the preservative solutions although the solutions influence in a marked degree the rates of haemolysis. The rise in the plasma potassium luvel exhibits two phases. It rises very rapidly for the first ten days of storage, increasing to 12 times the initial concentration in that brief period, after which the change is by comparison much slower. Variation in storage temperature has a greater effect relatively on the increase in the extra-cellular potassium concentration than daily shaking. The plasma calcium level falls by about 25 per cent of the original quantity and then begins to rise when the blood starts to haemolyse. It is suggested that it is the ionised calcium that is affected in this phenomenon. Storage at 38 degree Celcius hastens this fall and rise and so also does the effect of daily shaking.