Marker Assisted Selection (MAS) based on additive effects associated with alleles at marker loci, estimated by linear regression of individual phenotype on the markers, was applied to characters with non-additive gene action and non-additive environment. The base population was the F2 generation of a cross between two inbred lines. Computer simulations of MAS were conducted for characters with dominance, epistasis and genotype-environment interaction approximated by the 'additive-multiplicative' model. MAS was more effective than purely phenotypic selection in all cases. The efficiency of MAS for characters with non-additive gene action is comparable to (and for negative dominance even higher than) the efficiency of MAS for strictly additive characters. Environmental non-additivity, however, lowers the efficiency of MAS. Almost all results concerning the efficiency of MAS in our previous simulations of purely additive traits are applicable to non-additive traits.