Changes of mitochondrial and cytoplasm tumor metabolism were studied in malignant gliomas and normal cortex probes in vitro. By spectrophotometric methods marker enzymes of different mitochondrial (whole respiratory chain, citrate acid cycle, fatty oxidation) and cytoplasm (glycolysis, pentose phosphate shunt) metabolic energy pathways were analysed. Generally, the activities of intramitochondrial key enzymes were significantly decreased in gliomas when compared with enzyme activities of normal cortex tissue (p < 0.01). Glycolytic enzymes and a representative of the pentose phosphate shunt were unchanged or increased. Ratios of marker enzymes of the glycolytic pathway (lactate dehydrogenase) and glycose-6-P dehydrogenase revealed a significant difference between glioblastomas (p < 0.05) and grade III (p < 0.05) tumors in comparison to normal astrocytic tissue and astrocytomas WHO grade II. Thus, biochemical analyses allow metabolic grading of gliomas in vitro and may be a useful tool for understanding tumor biology.