Laser Doppler flowmetry (LDF) was used to study acute ipsilateral and contralateral disturbances of regional cerebral blood flow (rCBF) in a rat model of cerebral cortical contusion trauma. Twelve rats were intubated and artificially ventilated during and after trauma. Injury was produced with a weight drop technique (21 g from 35 cm) allowing 1.5 mm maximum compression of the right parietal cortex. Stationary laser Doppler probes were used for continuous blood flow measurements on the ipsilateral side adjacent to the traumatized tissue and on the contralateral side. Within 2 min blood flow decreased to 60% (+/- 9%) of the pretrauma rCBF level on the ipsilateral side and remained at this level for at least 20 min. On the contralateral side there was an initial increase to 172% (+/- 27%) at 4 min. This hyperperfusion phase was followed by a mild hypoperfusion phase with a flow of 78% (+/- 8%) of baseline, lasting approximately 60 min. An attempt was made to measure rCBF++ within the trauma site using a removable probe. We found that probe replacement in traumatized (as compared to control) animals caused a baseline shift with a considerable variability making interpretation difficult. However, the pattern of rCBF change did not differ from the measurements adjacent to the injury site. We tentatively conclude that the posttraumatic hypoperfusion phase was similar within the trauma region. The observed rCBF changes following trauma are similar to those seen following cortical spreading depression (CSD). We propose that CSD, known to occur on the ipsilateral side in our model, is one of the factors involved in acute blood flow decreases seen following cerebral trauma.