To investigate the hypothesis that the regenerating liver undergoes intracellular alkalinization during the prereplicative period, we measured intracellular pH (pHi) after partial hepatectomy in the rat. pHi was studied in livers from female Wistar rats perfused in situ with buffer containing HCO3-/CO2. The multiple indicator-dilution technique was used to determine pHi from the distribution volume of dimethyloxazolidine-2,4-dione (DMO). Perfusion conditions influenced pHi. There was a curvilinear relationship between pHi and flow rate and a linear relationship between pHi and temperature. Under equivalent perfusion conditions there were no significant differences between pHi in normal livers (7.27 +/- 0.02) and that following partial hepatectomy (7.27 +/- 0.03 at 0 h, 7.27 +/- 0.04 at 4 h, 7.28 +/- 0.03 at 8 h, and 7.31 +/- 0.02 at 24 h) or sham surgery (7.27 +/- 0.04 at 4 h, 7.33 +/- 0.08 at 24 h). Therefore intracellular alkalinization does not occur following partial hepatectomy and is unlikely to be a signal for regeneration.