In this paper, the Three Stage Polymerization Model (TSPM) proposed in our previous publication for free radical homopolymerization was extended to describe high-conversion copolymerization reactions exhibiting a strong gel effect. Moreover, the literature data on conversion history for styrene (St)-methyl methacrylate (MMA), MMA-ethylene glycol dimethacrylate (EGDMA) and acrylonitrile (AN)alpha-methylstyrene (AMS) copolymerizations were used to examine applicability of the model. It was found that TSPM is still suitable for kinetic description of the copolymerization systems mentioned above. (C) 2003 Elsevier Science Ltd. All rights reserved.