Rats were subjected to standard conditions of hemorrhagic shock. Animals were sacrificed 5 minutes and two hours after reinjection of blood which had effused into a syringe. The extent of shock was determined by measuring the acid base balance of the serum. Cerebral concentrations of NE, DA, DOPAC, HVA, 5-HT and 5-HIAA were measured and compared to controls. There was a significant decrease of the NE concentration and a highly significant increase of that of DA. Although the DOPAC concentration varied to a slight extent, that of HVA was significantly depressed 5 min after reinjection and exceeded initial values two hours later. It is consistent to interpret these results as a synaptic quiescence of DA utilization, which is no longer methylated by COMT. After two hours, however, extraneuronal DA metabolism was greatly increased, as indicated by the decreased DA concentration and the considerable increase of HVA levels. 5-HT turnover seemed to follow the same temporal variations, decreasing in the acute phase and then increasing during the recovery phase.