Rats rendered hypotensive and acidotic by withdrawal of blood were treated by infusion of either an equimolar mixture of sodium bicarbonate and sodium carbonate ("Carbicarb"), sodium bicarbonate alone, or sodium chloride. Skeletal muscle intracellular pH (pHi) was measured using magnetic resonance spectroscopy from the chemical shift of the carbon-2 (C2) proton resonance of the imidazole ring of anserine. In the groups treated with alkali, arterial blood pH (pHa) was restored to normal, but no change was observed in the sodium chloride-treated animals. Despite an elevation of arterial blood partial pressure of CO2 (PaCO2) in the group treated with sodium bicarbonate, no significant change in pHi was observed in any group. Blood lactate levels, initially elevated in all groups, underwent only minor changes. In all three groups a transient and similar elevation of arterial blood pressure was observed after infusion. Differential effects of Carbicarb and sodium bicarbonate in metabolic acidosis may be dependent on the model of metabolic acidosis used, and an alteration in PaCO2 induced by alkali therapy may not be a major determinant of changes in pHi.