Short interspersed repetitive elements (SINEs) were isolated from the equine genome and characterized. The equine SINE (ERE-1) family has several features characteristic of tRNA-derived retroposons. The five members of the equine family of SINEs are approximately 230 nucleotides in length and terminate with a sequence rich in oligo(A). They are all flanked by direct repeats at the 5' and 3' ends, and such repeats are the hallmarks of retroposons. In addition, the ERE-1 family has a tRNA-related region, which is similar to tRNA(Ser) of Drosophila (65% identity). tRNA(Ser) is a novel tRNA with respect to the origin of SINEs and has not previously been recognized among the twenty tRNA-derived SINEs characterized to date. The members of the ERE-1 family were found to be distributed among five species in the genus Equus, and their amplification may have contributed to the genetic variability of their hosts during evolution.