The effects of a metabolic and respiratory acidosis and alkalosis on intracellular pH (pHi) and K+ have been compared in cardiac and skeletal muscle from the anesthetized rabbit. The extracellular space and pHi were calculated from the distribution volumes of [51Cr] EDTA and [14C]DMO, respectively. When pHe was varied by altering PCO2, the slope of the line relating pHi to the extracellular pH (pHe) was greater (P less than 0.05--0.001) than that obtained during metabolic changes of pHe in right and left ventricles, atria, diaphragm, and quadriceps. During metabolic acidosis and alkalosis, the slope of pHi/pHe line did not vary between tissues. During respiratory acidosis, there was no difference in slope between cardiac tissues, but it was less in left ventricle than quadriceps (P less than 0.001). In left ventricle intracellular K+ increased in a metabolic (P less than 0.05) or respiratory acidosis (P less than 0.02), whereas in diaphragm it decreased (P less than 0.02). Intracellular K+ correlated with pHe and pHE-PHi. Changes in pHi but not intracellular K+ could explain known differences in myocardial function in respiratory and metabolic acidosis.