The effect of changes in blood pH on the distribution of d-tubocurarine within the plasma was investigated in 12 animals. Using a modified Latin square design each dog was studied for 1 hour under conditions of normal blood pH, respiratory acidosis, and respiratory alkalosis. Circulatory depression was prevented by the infusion of 1,1-dimethy1–1,4-phenylpiperazinium (DMFP). Plasma levels of d-tubocurarine were measured spectrophotometrically at 3, 5, 10, 20, 30, and 60 minute intervals following the intravenous injection of 0.3 mg./kg. An analysis of variance indicates no significant difference between plasma concentrations of d-tubocurarine at various pH levels and suggests that changes in blood pH in the physiologic range have little effect on the plasma distribution of d-tubocurarina