Autoregulation and CO2 response of cortical blood flow and their relationship to cortical oxygen tension is not fully known. We have examined autoregulation and CO2 response of local cortical blood flow (CoBF) and cortical oxygen tension (bPO2), using 41 New Zealand white rabbits. CoBF was measured continuously by using the heated thermocouple technique and bPO2 was monitored by the polarographic method. Intravenous injection of phenylephrine hydrochloride or trimethaphan camsylate was used to test for autoregulation by increasing or decreasing perfusion pressure. The data was analyzed in the range between 50 and 140 mmHg of mean arterial blood pressure (MABP). The range of autoregulation was determined by our own analytical method. PaCO2 was manipulated between 18.3 and 63.2 mmHg. It was increased by raising the concentration of CO2 in the inspired gas mixture. Hypocapnia was induced by hyperventilation. The mean values of CoBF and bPO2 were 36.2 +/- 5.3 ml/100 g/min and 32.9 +/- 12.8 mmHg respectively at 90 mmHg of MABP during the test for autoregulation. The changes in both CoBF and bPO2 with changing perfusion pressure were often relatively small at near baseline blood pressure and became more pronounced with large increase or decrease in MABP. On returning from high MABP to baseline blood pressure, a hysteresis effect on CoBF was observed in 20 out of twenty two cases. The autoregulation of CoBF was maintained in the range between 80 and 100 mmHg of MABP. On the other hand, bPO2 was maintained constant in the range between 75 and 110 mmHg of MABP.(ABSTRACT TRUNCATED AT 250 WORDS)