Lonidamine (LND) has been shown to inhibit tumor aerobic glycolysis. Its effect was evaluated on several human astrocytomas at different degrees of malignancy; a correlation was found between LDN effect on lactate production and tumor malignancy: in grade I and II astrocytomas LND stimulates lactate production, while in grade III, IV and glioblastoma multiforme lactate production is inhibited. In an attempt to explain this different behaviour, hexokinase content and compartmentation was evaluated in astrocytomas from fresh operatory specimens and from cultured cells as well, observing a significative correlation between malignancy, hexokinase activity, percent of mitochondrially-bound hexokinase and LND effect. The results justify from a biochemical point of view the role of LND as a 'non-conventional' agent in multimodality combined treatment for malignant gliomas.