BACKGROUND: Everything on the earth can be affected by gravity of the earth. So, microgravity, as small as 10 minus 3 times G, can make some effects to the growth or maturation of cells. Under this hypothesis we examined cell proliferation and chemosensitivity after exposure to simulated microgravity using the malignant glioma cell lines. We exposed cells to simulated microgravity using a 3D-clinostat which is a type of rotating culture system that has two independent axes of rotation to disperse the gravity vector throughout the whole steric angle. METHODS: D54MG, U251MG and T98G cell lines were used in this study. All samples were identically treated before the start of the experiment and randomized for clinorotation (CL group) or culturing at 1G (C group). The Opticell cell culture system, mounted in a 3D-clinostat, was used for culture under simulated microgravity. Cells were cultured under a 1G environment for 24 h before using the 3D-clinostat to achieve adhesion. Morphological changes in glioblastoma cells during culture were examined using an inverted phase-contrast microscope. We analyzed the viability of the CL group and the C group cells by Trypan-blue exclusion method. The mitochondrial membrane potential was measured using the fluorescent dye Rhodamine123. Cell cycle distribution was measured with a FACS Caliber flow cytometer. Immunoblotting and sensitivity to CDDP was examined. RESULTS: Proliferation was significantly lower in all cell lines in the CL group compared to the C group on day three. The percentage of living cells in the CL group showed no significant differences compared to the C group. Cell cycles indicated by flow cytometry showed no differences between the CL and C groups. In both groups, FACS analysis also showed there was no significant proportion of apoptotic cells in any of the cell lines. In the CL group, significant deterioration of mitochondrial activity was shown in all malignant glioma cell lines compared to the C group. CONCLUSIONS: This is the first study to examine the effect of simulated microgravity on the proliferation, mitochondrial activity, and chemosensitivity of human malignant glioma cells. Our data suggests that simulated microgravity induces growth inhibition through reduction of mitochondrial activity, and enhances the chemosensitivity of malignant glioma cells to CDDP. Our findings using 3D-clinorotation provide new insight into the responses to simulated microgravity of malignant glioma cells. SECONDARY CATEGORY: Tumor Biology.