The effect of different concentrations of thiophosphamide on chromosomes of human lymphocytes within 1 hour at the G0 phase under different temperatures was investigated. It is shown that the concentration curves of the effect of thiophosphamide under different temperatures can be described according to the equation: A= =exp [-(KC+alpha)2], X=exp [(KC+alpha)2]-1, where A is the portion of normal cells, X is the number of chromosome breaks per cell, C is the concentration of thiophosphamide, K and alpha are coefficients. The coefficient alpha was shown not to depend on temperature under the action of thiophosphamide on cells. The temperature dependence of the coefficient K can be described according to Arrenius equation: K=A exp [-deltaU/RT]. Proceeding from the experimental data the changes of entropy, free energy and energy of activation of thiophosphamide-chromosome interaction were calculated (deltaS= =18.48 cal-mol-1-degree-1, deltaF310=12897.40 cal-mol-1, deltaU=18626.20 cal-mol-1 for the test "aberrant cells"; deltaS=17.79 cal-mol-1-degree-1, deltaF310=12935.02 cal-mol-1, deltaU= =18449.92 cal-mol-1 for the test "chromosome breaks". These values of thermodynamic potentials show that the reaction of thiophosphamide-chromosome interaction can be of the fermentative nature.