The aim of the study was to monitor brain metabolism during aneurysm clipping using microdialysis and multiparameter sensors, particularly to investigate the effects of temporary clipping of vessels. Microdialysis catheters (n = 10) and Paratrend brain multiparameter (O2, CO2, pH and temperature) sensors (n = 15) were inserted into the cerebral cortex via a specially designed triple bolt prior to craniotomy. Baseline brain O2 levels ranging from 15-45 mmHg (2.0-6.0 kPa) and glucose levels from 0.5-3 mmol l-1 were stable during uneventful periods. The mean lactate/pyruvate (L/P) ratio ranged from 32 to 65 (normal < 30), indicating a tendency towards anerobic metabolism in all patients. Overall, short periods of temporary clipping (< 3 min; n = 6) were well tolerated producing no significant reduction in brain O2 (pre-clip mean 23 mmHg (3.0 kPa) vs. post-clip mean 20 mmHg (2.6 kPa)) or elevation of the L/P ratio (pre-clip mean 42 vs. post-clip mean 43). Two patients with prolonged temporary clipping showed derangements in the Paratrend parameters associated with increases in the L/P ratio. The results demonstrated that the monitored variables remained stable during uneventful procedures, including transient temporary clipping, but adverse events such as prolonged temporary clipping resulted in pronounced changes in brain metabolism. Monitoring of metabolism during aneurysm surgery may be of benefit in selected patients.