There are six possible types of gene interaction in qualitative traits, namely, complementary, duplicate, cumulative, dominant epistasis, recessive epistasis and inhibiting. In genetic studies, the problem of mapping interactive genes may be met sometimes, but no systematic researches on the methodology and computer software for the mapping of interactive genes have been reported up to date. In this paper, methods for the mapping of interactive genes based on maximum-likelihood estimation and corresponding computer software (IGMapping 1.0) are presented. Computer simulations have shown that the methods proposed can unbiasedly estimate the recombination frequency or linkage distance between a codominant marker and an interactive gene.