The process of coalescence or breakup of drops in turbulent flow is of importance in many technical applications. A new size distribution takes place due to the coalescence or the breakup of the drops during the motion of a dispersed system. Based on the experimental data given in the literature, some new empirical relationships are developed in this paper to evaluate the maximum stable drop sizes, the coalescence frequencies and the drop size distribution in an isotropic turbulent flow. The relationships are developed essentially in terms of the particle Reynolds number or of the physical properties of the system. The Focker-Planck equation is used to estimate the particle size distribution. The model predictions are compared with the experimental data given in the literature. The results indicated that the predicted values and the experimental data are in a good agreement. (C) 2002 Elsevier Science B.V. All rights reserved.