EN
Magnetoreflectance of free exciton and magnetization in Zn_{1-x}Mn_{x}Se (0.0007 < x < 0.12) were measured. The evaluated proportionality factor between the exciton splitting and the magnetization showed a strong concentration dependence. This effect cannot be explained within the mean field approximation and the virtual crystal approximation and it was described within the model including chemical and magnetic disorder.