Methods of correction for intracellular pH (pHi) estimation from the absorbance of the pH-sensitive dye, 4',5'-dimethyl-5-(and -6-) carboxy-fluorescein (Me2CF), were described. In the guinea-pig vena cava, a reasonable estimation of pHi changes was obtained when the distortion of the spectrum was corrected using the tissue absorbance at wavelengths longer than 570 nm.