LTR retrotransposons of the Tf1/sushi group from a diversity of vertebrates, including fish, amphibians, and mammals (humans, mice, and others), are described as full-length or partial elements. These elements are compared, and the mechanisms involved in self-priming of reverse transcriptase and programmed phase shifting are inferred. Evidence is presented that in mammals these elements are still transcriptionally active and are represented as proteins. This suggests that members of the Tf1/sushi group are present as functional elements (or incorporated as partial elements into host genes) in diverse vertebrate lineages.