Seven hundred and ninety Drosophila melanogaster genes, alternatively spliced in coding regions were considered together with their Drosophila pseudoobscura orthologs. It was found that nucleotide substitutions in alternative coding regions accumulate more intensively than in constitutive regions. Moreover, the evolutionary pattern of alternative regions depends on their inclusion mechanisms (use of alternative promoters, splicing sites or polyadenylation sites) significantly. The rate of synonymous substitutions varies is more dramatically than that of nonsynonymous substitutions. Nucleotide substitution patterns in different classes of alternative regions of mammalian and Drosophila genes have little in common.