Glioblastoma multiforme is characterized as highly invasive and rapidly growing astrocytomas, and scientists have sought for efficient treatment against malignant gliomas for a long time. Therefore, we compared the respond of rat glioma (C6) and glioblastoma multiforme cells derived from two patients to vitamins K-1 K-2 and K-3 The cells were exposed to 100, 250, 500, 750 and 1000 muM of vitamins K-1 and K-2, and 1, 10, 25, 50, 75 and 100 muM of vitamin K-3 for 24 hours in an incubator atmosphere of 5% CO2, 37 degreesC and 100% humidity. Cell viability was estimated by MTT assay. Vitamin K, showed no growth effect on all the glioma cells examined. Vitamin K-2 did not cause any change in number of C6, however induced growth inhibition in a dose-dependent manner on glioblastoma multiforme. The IC50 values of vitamin K-2 were 960 muM and 970 muM for glioblastoma multiforme, respectively. Vitamin K, had also growth inhibitory effect in a dose-dependent manner on both C6 and glioblastoma multiforme. The IC50 values were 41 muM, 24 muM and 23 muM for vitamin K-3, respectively. We concluded that vitamin K-3 is more effective than vitamin K-2 for inhibition of cancer cell growth, and might have an alternative value as an anticancer drug against glioblastoma multiforme.