Patients and Interventions. Tissue damage caused by brain retraction was evaluated utilizing intracerebral microdialysis in six patients operated on subfrontally for pituitary adenoma. The microdialysis probes (membrane length 10 mm, cut-off 20 kDalton) were placed in cerebral cortex beneath the brain retractor and perfused with Ringer solution at 0.3 mul/min. The microdialysis vials were changed at intervals of 30 minutes and analysed for glucose, pyruvate, lactate, glutamate and glycerol. Results. During brain retraction regional intracerebral glucose was within normal range in cortical tissue and the levels of lactate, glutamate, and glycerol as well as the lactate/pyruvate ratio were considerably above normal range. Conclusion. The biochemical analysis shows a pronounced incomplete cerebral ischemia due to brain retraction. The increases in glutamate and glycerol indicate tissue damage and degradation of cell membranes. Intracerebral microdialysis may be a valuable tool in the development of optimal techniques for brain retraction during neurosurgical procedures.