The c-abl gene encodes a protein tyrosine kinase and is transcribed from at least two promoters giving rise to transcripts of two size classes of approximately 5 and 6 kb in length. These mRNAs only differ in their most 5' exon and encode proteins of similar size but with different N-termini. In the mouse testis an additional abundant c-abl mRNA of 4 kb is detected. This mRNA was shown to be expressed in the haploid male germ cells of the adult mouse. Here we describe the cloning and molecular characterization of a cDNA representing the testis specific c-abl transcript. We show that the 4 kb c-abl mRNA arises from alternative polyadenylation of an RNA transcribed from the same promoter as the 5 kb mRNA. The site of polyadenylation is unusual in this shorter transcript as it is not preceded by the highly conserved hexanucleotide AAUAAA. The use of this polyadenylation site removes 1.2 kb of 3' sequences present in the somatic c-abl mRNAs, but does not affect the main open reading frame of the transcript. Using in situ hybridization on whole testis sections it is shown that the 4 kb c-abl mRNA is most abundant in the elongating spermatids.