The quantitative mechanistic acid-base approach to clinical assessment of acid-base status requires species-specific values for A_tot (the total concentration of nonvolatile buffers in plasma) and Ka (the effective dissociation constant for weak acids in plasma). The aim of this study was to determine A_tot and Ka values for plasma in domestic pigeons. Plasma from 12 healthy commercial domestic pigeons was tonometered with 20% CO₂ at 37°C. Plasma pH, Pco₂, and plasma concentrations of strong cations (Na, K, Ca), strong anions (Cl, L-lactate), and nonvolatile buffer ions (total protein, albumin, phosphate) were measured over a pH range of 6.8 to 7.7. Strong ion difference (SID₅ = Na + K + Ca- Cl -lactate) was used to calculate A_tot and Ka from the measured pH and Pco₂ and SID₅. Mean (± SD) values for bird plasma were: A_tot = (7.76 ± 2.15) mmol/l (equivalent to 0.32 mmol/g of total protein, 0.51 mmol/g of albumin, 0.23 mmol/g of total solids); Ka = (2.15 ± 1.15) x 10^-7; pKa = 6.67. The net protein charge at normal pH (7.43) was estimated to be 6 mEq/l; this value indicates that pigeon plasma has a much lower anion gap value than mammals after adjusting for high mean L-lactate concentrations induced by restraint during blood sampling. This finding indicates that plasma proteins in pigeons have a much lower net anion charge than mammalian plasma protein. An incidental finding was that total protein concentration measured by a multi-analyzer system was consistently lower than the value for total solids measured by refractometer.