Dogs anesthetized with halothane were subjected to stress by increased depth of anesthesia, arterial hypoxemia, or hemorrhagic hypotension in stages leading ultimately to death. Excess lactate (XL) in the whole body, splanchnic circulation, and skeletal muscle did not change significantly until the final period just preceding death. At this time XL for the whole body and the splanchnic circulation increased. Muscle XL did not increase in any circumstance tested despite compromise of O2delivery sufficient to decrease muscle μo2. Overall, changes in arterial blood pH, buffer base, lactate, and Iactate/pyruvate ratio were small, metabolic acidosis was minimal to absent, and XL was insensitive and fallible as an index of regional and whole-body hypoxia. These findings are believed to be directly related to the relative suppression of activity of the sympathetic nervous system during halothane anesthesia.