The nucleation and growth kinetics of several binary organic melts (naphthalene/diphenyl, trioxane/water, p-dichlorobenzene/m-dichlorobenzene, caprolactam/water) were investigated using an isoperibolic reaction calorimeter. Based on the released heat of the crystallization process. the course of the supersaturation could be determined. By using momentum equations, and by applying a backward calculation, the growth and nucleation rates have been deduced from the final crystal size distribution. The experiments were carried out for batch cooling modes in agitated suspensions, by varying systematically, the supersaturation and the impurity content. A decreasing amount of impurities, leads to an increase of growth rates, and to a decline of nucleation rates. By introducing a dimensionless variable. the relative purity, the influence of the impurities on the growth and nucleation kinetics could be generalized. Further kinetic data on pure substances which are difficult to measure could be derived.