The aim of the study was to evaluate an experimental approach based on a fluid percussion rat trauma model in combination with the microdialysis technique for the analysis of cerebral interstitial biochemical alterations following head trauma, and to test the hypothesis that the previously observed acute accumulation of lactate and increase in the lactate pyruvate ratio may persist for several days following trauma. We analyzed how lactate, pyruvate, and glucose were altered in the cortex adjacent to the contusion and in the contralateral side of the brain following a traumatic brain injury. The results were compared with those from sham-operated animals. The lactate concentration in the cortex adjacent to the contusion was 0.73 +/- 0.13 mmol/L and 0.71 +/- 0.08 mmol/L 24 and 48 h posttrauma, respectively, and 0.42 +/- 0.07 mmol/L in the sham group (p < 0.05). The lactate/pyruvate ratio of 18.3 +/- 2.3 in the cortex adjacent to the contusion 24 h posttrauma was higher than corresponding value of 10.3 +/- 1.5 in the sham group (p < 0.05). The lactate/pyruvate ratio 48 h posttrauma did not differ from that in the sham group. Interstitial glucose in the cortex adjacent to the contusion and the sham group were similar. Microdialysis measurements from the contralateral side did not differ from those in the sham group. We conclude that the previously observed acute alterations in brain metabolism persist for at least 48 h posttrauma. Further, the measured parameters from the contralateral side can be used as controls since they did not differ from the sham group. Combining microdialysis with a fluid percussion trauma model may be a tool to explore secondary brain injury mechanisms and evaluate new therapies for the treatment of traumatic brain injury.