Whether they are of low or high histopathological grade, human astrocytic tumors are characterized by a marked propensity to diffuse into large areas of normal brain parenchyma. This invasion relates mainly to cell motility, which enables individual cell migration to take place. The present study characterizes in vitro the gastrin-mediated effects on both the growth (cell proliferation vs. cell death) and motility dynamics of the human U87 and U373 glioblastoma cell lines. A computer-assisted phase-contrast microscope was used to track the number of mitoses versus cell deaths every 4 min over a 72-h period and so to quantitatively describe the trajectories of living U373 and U87 cells growing on plastic supports in culture media both with and without the addition of 0.1, 5, or 100 nM gastrin. While 5 or 100 nM gastrin only weakly (p < .05 to p < .01) increased cell proliferation in the U87 cell line and not in U373 one, it very significantly (p < .001) inhibited the amount of cell death at 5 and 100 nM in both the U87 and U373 lines. In addition, 5 nM gastrin markedly inhibited cell mobility in U87 (p < .00001) and U373 (p < .0001) glioblastoma models. All these data strongly suggest that gastrin plays a major role in the biological behavior of the in vitro U87 and U373 human glioblastoma cell lines in matters concerning their levels of cell motility and growth dynamics.