The authors have studied the characteristics of the scatter of light by cell suspensions in norpemal conditions (pH 7·2; 20 °C) and on exposure to external agents (change in pH, rise in temrature). It is shown that in normal conditions for large cells (radius 3-7 μ) the turbidity weakly depends on 1/λ; power n = 0·2-0·3. On damage to the cells the values of n rises and the course of the dependence coincides with the character of the increase in the fraction of damaged cells determined from the eosin test. The changes in the parameters of the total light scatter on damage to the cells are related to the increase in the contribution of scatter by the intracellular microstructure.