Metalorganic vapor-phase epitaxy of ternary ZnMgSe and ZnCdSe layers, quaternary ZnMgCdSe layers and superlattices on InP (1 0 0) is presented. The dependence of the Cd- and Mg-incorporation into the ternary compounds on the molar ratio in the vapor phase, and the influence of the buffer material and the growth conditions on the structural quality are discussed. A tendency to segregation and increased mosaicity is found in quaternary ZnMgCdSe structures with magnesium fractions exceeding 40%, evaluated by X-ray diffraction, photoluminescence and transmission electron microscopy.