Some naturally occurring plasmids like ColEl and ColK have been found to harbor site-specific recombination sequences, the core regions of such sequences have shown 82% homology when so aligned. The high degree of homology was the basis for testing the possibility of recombination between them. The sequences were cloned in the vector pUC18 in opposite orientation and introduced into E.coli cells and the analysis of the DNA harvested from the transformed cells showed that the sequences had undergone recombination, such recombination, such recombination was of the site-specific mode. No sequence deletion was detected, as was the case with such sequences when they were in the same orientation, Interestingly the event of recombination in this case resulted in the inversion of the region located between the recombination sites of the two cloned fragments.