1. When saponin or sodium taurocholate are used as haemolysins for human red cells, the effect of temperature on the haemolytic process cannot be adequately described by the Arrhenius equation.
2. The failure of this equation to describe the results is due to the fact that changes of temperature affect several constants in the equation for the reaction between the lysin and the cells and not the velocity constant only.
3. It is shown that the changes of temperature produce irreversible changes both in the cells and in the lysin, which fact adds to the difficulty of analysing the results.