Statistical-mechanical expressions for the chemical potential of a dispersed particle, for the Gibbs energy of dispergation, and for the activation energy of dispergation are derived for a monodisperse system with a liquid continuous medium and a solid or liquid dispersed phase. The work of dispergation is calculated as a function of the size of dispersed particles with taking into account the dependence of surface free energy on the particle size and the interaction between particles in the form of the hard sphere potential. The boundary of the region of spontaneous dispergation and the condition for the realisation of stable states in the process of dispergation are formulated. Copyright (C) 1999 Elsevier Science B.V.