The chicken c-mil gene produces two mRNA species generated by an alternative splicing mechanism. These two transcripts differ at least by the presence or absence of a 60 nucleotide exon (E7a) localized at the splice junction of c-mil exons 7 and 8. By using RNAase protection assays, we have analysed the pattern of expression of these two mRNA species in several chicken tissues. Here we report that the two c-mil mRNAs are differentially expressed in chicken tissues: the mRNA lacking E7a is detected in all tissues tested, while the mRNA containing E7a is detected only in the skeletal muscle, heart and brain. Sequences homologous to E7a have also been detected in DNAs from quail, mouse and human cells and their sequencing revealed that the alternative E7a is structurally preserved in these species. By PCR analyses performed on RNAs extracted from muscular tissues of these species, we also show that the alternative splicing mechanism described in chicken also occurs in these species.