Once freezing and thawing the yeast leads to incomplete destruction of the cell membrane and to too low values of the cell pH determined in the cell suspension with the glass electrode. The cells are rendered completely permeable through boiling, treatment with acetone, or freezing and thawing the cell repeatedly. Cell pH’s obtained in this ways are definitely higher. The differences in cell pH’s observed with completely broken cells and partly broken cells can be accounted for quantitatively to the presence of intact cells in the only once frozen and thawed cell suspension.