The objective of this research was to isolate and characterize Ty3/gypsy sequences in culti-vated allotetraploid cotton, Gossypium barbadense L. Using a degenerate oligonucleotide designed to amplify these sequences by PCR, part of the reverse transcriptase gene of Ty3/gypsy retro-transposons was isolated, cloned, and sequenced. These retro-elements exist in the cotton genome in high copy number, and their encoded transcripts were detected. Phylogenetic analysis shows that these retro-elements are heterogeneous and closely related to elements present in other plant species. These results indicate that Ty3/gypsy retro-transposons are standard component of the Gossypium genome, and support the fact that Ty3/gypsy retro-transposons represent a major component of the plant genome. R etro-elements and their derivatives are ubiquitous