Two sublines of B16 melanoma cells, F10 and BL6, are metastatic after intravenous injection, but only BL6 cells are metastatic after subcutaneous injection. We found a new member of the GTPase superfamily, namely TIB929, which displayed an induction of expression in BL6 cells. It conserved three consensus sequences for GTP-binding site motifs and showed a significant homology to the yeast Gtr2 gene throughout the coding sequence. TIB929 was expressed ubiquitously in human tumor cells, with a marked expression in highly metastatic cells. TIB929 was mapped on mouse chromosome 4D, syntenic to human chromosome 1p. The results suggested an involvement of TIB929 in malignant progression.