Two related families of transposons were isolated from schizosaccharomyces pombe, an organism which has been the object of extensive genetic studies which had previously produced no evidence for the existence of such elements. These two classes of repeated DNAs, dubbed Tf1 (transposon of fission yeast 1) and Tf2 have many properties of retrotransposons. Tf1 and Tf2 both possess long terminal repeats and predicted protein sequences that resemble the protease, reverse transcriptase, and integrase domains of retroviruses. The chromosomal locations and total numbers of Tf1 and Tf2 differ greatly in various isolates of S. pombe. The Tf elements are expressed in the form of 4.5-kb mRNAs. The complete sequence of Tf1 was determined and suggests that a novel mechanism for regulating its gene expression may be used.