1. The effect of metabolic acidosis of 4–6 h duration on cardiac output, blood pressure, heart rate, and hepatic and renal blood flow has been studied in the rat.
2. In anaesthetized rats, blood pressure and heart rate fell linearly with blood pH in both sham-operated and nephrectomized rats. There was no significant difference between the two groups in the effect of acidosis on either variable.
3. Cardiac output showed a significant fall with increasing acidosis in the conscious rat.
4. Estimated hepatic blood flow in conscious rats showed a significant positive correlation with blood pH in both sham-operated and nephrectomized animals. There was no significant difference in estimated hepatic blood flow between the two groups of animals at any blood pH.
5. In conscious rats, increasing acidosis caused a progressive decrease in estimated renal blood flow.
6. It is concluded that the increase in the previously described apparent renal contribution to lactate removal in the acidotic rat cannot be explained by any circulatory effect mediated by the kidney. The possible relevance of the findings to lactate homeostasis is discussed.