The reaction ensemble Monte Carlo method is used to study chemical equilibrium in Lennard-Jones fluids confined in slitlike pores. An impact of an external field on the chemical equilibrium is being discussed. The results are compared with the bulk system behavior. The composition of equilibrium mixtures is determined for various values of parameters characterizing the system. The scaling particle-Monte Carlo (SP-MC) method is applied to evaluate the excess chemical potential in equilibrium mixture. These values are used to calculate the reaction constant. (C) 2001 American Institute of Physics.