Loss of chromosome 10 was observed in 10 out of 12 xenografted glioblastomas studied. Chromosome 10 carries the gene coding the hexokinase type 1 isoenzyme (HK-I), which catalyses the first step of glycolysis, which is essential in brain tissue and glioblastomas. We investigated the relationships between the relative chromosome 10 number, the amount of HK-I mRNA, HK-I activity and its intracellular distribution, and glycolysis-related parameters such as the lactate-pyruvate ratio, lactate dehydrogenase (LDH) and ATP contents. Individual tumour HK-I mRNA amounts were 23-65% lower than that of normal human brain and reflected the relative decrease of chromosome 10 number (alpha < 0.01). Total HK activities of individual glioblastomas varied considerably but were constantly (a mean of seven times) lower than that of normal brain tissue. The mitochondria-bound HK-I fraction of individual tumours was generally over 50%, compared with that of normal brain tissue. As shown by lactate - pyruvate ratios, in all the gliomas, glycolysis was elevated to an average of 3-fold that measured in normal brain. An elevated ATP content was also constantly noted. Adaptation of glioblastoma metabolism to the chromosome 10 loss and to the HK-I transcription unit emphasises the critical role of glycolysis in their survival. We hypothesise that HK-I, the enzyme responsible for initiating glycolysis necessary for brain function, may approach its lowest limit in gliomas, thereby opening therapeutic access to pharmacological anti-metabolites affecting energy metabolism and tumour growth.