The Monte Carlo models of binary irreversible copolymeriza-tion with ultimate and penultimate effect are applied to the copolymerization of acrylic acid and methyl acrylate, and styrene and benzylidene malononitrile, respectively. The agreement with available experimental data is quite good. A comparative study between the formal kinetics model and the Monte Carlo model reveals that statements concerning the copolymer composition are robust, but statements concerning the sequence distribution are not always robust.