Some aspects of the histochemical technique for the detection of sodium ions with potassium antimonate have been analyzed. When potassium antimonate is used for the detection of sodium ions the pH should not decrease below 7.2 during fixation. Potassium antimonate was also precipitated by ethanol used for dehydration, resulting in dilution of the water used as solvent. This should not be confused with the histochemical product. Precipitate may be formed with calcium ions and magnesium ions. Potassium phosphate buffer used to control the pH seems to inhibit the precipitation reaction of potassium antimonate with sodium ions; the nonbuffered fixative produces a good result at the electron microscopic level.