It has been shown that the usage of weak sinusoidal electric fields with sinusoidal amplitude modulation in studies of electroorientational effects in colloids and suspensions make it possible to determine the particle size distribution and investigate their induced and permanent dipole moments. This method is designed for study of disperse systems with high electroconductivity including biocolloids, cell-like suspensions and solutions of macromolecules. In this paper the results of experiments on polydispersity of aqueous colloid of palygorskite and aqueous suspensions of E. coli and Ps. fluorescens are presented.