Measurement results of barium sulphate reaction crystallization kinetics are presented. The experiments were carried out in the crystallizer with internal circulation of suspension. The crystallizer was continuously fed with barium chloride solution (of concentration 24.0 mass%) and stoichiometrically equivalent amount of crystalline ammonium sulphate. The BaSO4 crystals' nucleation and growth rates were estimated from the crystal size distributions (CSDs) taking into account a size dependent growth (SDG). The research results may be utilised in the technology of used quenching salts' processing. (C) 2004 Elsevier B.V. All rights reserved.