Cartilage is an avascular tissue, the cells of which are exposed to reduced extracellular pH. The synthesis of cartilage matrix by chondrocytes is pH-sensitive and therefore control of intracellular pH (pHi) is important. We have measured the pHi of chondrocytes in MOPS-buffered saline (pH 7.4) using the fluorescent dye 2',7'-bis-2-(carboxyethyl)-5(6)-carboxyfluorescein. Mean pHi was 7.10 +/- 0.04 (+/- S.E.M., n = 22), and intracellular buffering power was 30 +/- 4 mmol l-1 (pH unit)-1 when pHi was displaced over the range 7.4-7.8 (n = 13). Recovery from acid load was blocked by 100 microM-ethylisopropylamiloride or by removal of extracellular Na+, indicating that these cells possess the Na(+)-H+ antiporter.