Recent animal research has provided evidence that brain ischaemia is associated with a shift of energy related metabolites (lactate, adenosine, inosine, and hypoxanthine) and several transmitters from the intracellular to the extracellular fluid (ECF). These chemical changes of the ECF reflect the energy crisis of the ischaemic tissue. We have proposed that measurement of these metabolites in the ECF using microdialysis may be a useful technique for detection of secondary ischaemia in neurosurgical intensive care patients. As a first step in the evaluation of such a possible clinical application of microdialysis the aim of this study was to measure energy related metabolites and amino acid transmitters during cerebral ischaemia in man. Microdialysis probes were inserted in tumour-free cortical tissue in the frontal lobe in patients undergoing frontal lobe resection as a treatment for brain tumours. Dialysis samples were collected in 10 minutes fractions before and during frontal lobe resection, thus serving as a simulated ischaemia model. The resection procedure was associated with markedly elevated levels of the energy related metabolites as well as transmitter amino acids. The tissue surrounding the probes was examined histologically, and the degree of oedema was estimated from CT scans. In two of the patients the tissue hosting the probes was oedematous. These patients had markedly higher basal levels of lactate. The main conclusions were (1) that the results support the clinical potential of microdialysis, (2) that lactate may be a sensitive indicator of the metabolic disturbances associated with brain oedema, and (3) that frontal lobe resection may be a useful human brain ischaemia model.