Molecular mechanisms underlying the unique locomotion of highly motile free-living Amoeba proteus, a widely used model of amoeboid movement, still remain unknown. Recently, we have shown that blocking amoeba endogenous Rac-and Rho-like proteins led to the distinct and irreversible changes in the behaviour of these large locomoting cells and to a significant inhibition of their locomotion. To further elucidate the mechanism of Rho pathway, we tested the effect of introduction of active recombinant human RhoA and Rac1 proteins on amoebae cells. While the degree of the inhibition of migration of cells treated with both proteins seems to be similar to cells microinjected with anti-RhoA and anti-Rac1 antibodies, there are distinct differences in cell behaviour and morphology when compared with the blocked phenotypes. The results indicate the important and complex role of Rho-family proteins in amoebae migration.