Genome complexity and sequence arrangement in several Ranids (R. catesbiena, R. clamitans, R. pipiens pipiens, R. pipiens berlandieri) is presently being determined. The first three frogs display the "Xenopus" pattern (the presence of short interspersed repetitive sequences). The fourth frog has not yet been examined. Single copy homology studies are also in progress, using these four species. Sequence divergence in repetitive sequences of Xenopus laevis and Xenopus borealis is being analysed, using stringent criteria. The intention is the development of a more quantitative assay for the rate of divergence of repetitious sequences relative to that of single copy sequences.