1. Temperature induced changes in blood pH inD. dorsalis may be accounted for by constant plasma strong ion difference ([SID]), constant total weak acid concentration ([Atot]) and observed in vivo partial pressure of CO2 (\(P_{CO_2 }\)) (Fig. 1). I studied renal and cloacal function at different body temperatures (Tb) to learn how constant plasma [SID] is preserved. I considered acid and base excretion in terms of the independent variables of acid-base status: [SID], [Atot] and\(P_{CO_2 }\). I analyzed changes in urinary [SID] and [Atot] in terms of glomerular filtration and net postglomerular transport of strong ions (Na+, K+, Mg++, Ca++, Cl−) and uric acid. 2. Plasma [SID] did not change withTb (Table 1). The excretion of urine of constant [SID] at different temperatures, except for cooling to 18°C, is consistent with preservation of plasma [SID] between 25 and 42°C. 3. At different constantTb's net excretion of strong ions, uric acid and total CO2 of ureteral and cloacal urine increased with temperature. During changes ofTb between 25 and 42°C similar patterns were seen (Table 2). Increased excretion of solutes at higherTb's was accompanied by increased glomerular filtration rates (GFR) and relatively constant fractional excretion (Table 4). Constant [SID] of urine was due to parallel adjustments in the excretion of strong ions (primarily Na+, K+ and Cl−). 4. In contrast to water breathing animals, temperature induced changes in blood pH inDipsosaurus, over the short term, probably do not involve net extra-pulmonary excretion of CO2, strong ions, or weak acids. 5. Changes in\(P_{CO_2 }\) via changes in lung ventilation appear to be the major controlling element in temperature induced acid-base adjustments inDipsosaurus. This conclusion is discussed in terms of the normal thermal history ofDipsosaurus and the time courses of acid-base adjustments by the various organ systems in ectotherms.