The ammonium acetate saturation (AMAS) method was used to study the cation-exchange capacity (CEC) of zeolitic volcaniclastic materials from Santorini and Polyegos Islands, Greece. The AMAS method was tested with respect to the time required to saturate the samples of zeolites with ammonium (NH 4 (super +) ) ions, the efficient liberation of NH 4 (super +) ions, and the suitability of two widely used techniques to measure ammonia (NH 3 ) (Kjeldahl ammonia distillation technique and the ammonia electrode technique). By using the inductively coupled plasma-mass spectrometry (ICP-MS) technique and measuring the number of cations exchanged during ammonium acetate (NH 4 OAc) saturation, it was found that the saturation period for zeolitic materials must be increased to 12-day cycles to ensure effective saturation. Following NH 4 OAc saturation, the AMAS method produces NH 4 (super +) solutions, after the NH 4 (super +) -saturated samples of zeolites are washed with 10% NaCl. The amount of the NH 4 (super +) ions in solution (i.e., exchangeable cations) is a measure of the CEC. The NH 4 (super +) ions can not be directly measured and must be converted to NH 3 . The Kjeldahl ammonia distillation technique and the ammonia electrode technique for measuring NH 3 give identical CEC results. However, the ammonia electrode technique, when used directly with the NH 4 (super +) samples of zeolite without 10% NaCl treatment, generally gives higher CEC values. The amount of NH 4 (super +) treated (converted to NH 3 ), when the NH 4 (super +) -saturated zeolitized samples were used directly, was higher than the amount of the NH 4 (super +) treated when the NH 4 (super +) solutions were obtained after washing the NH 4 (super +) -saturated zeolitized samples with 10% NaCl. Therefore, washing with 10% NaCl does not facilitate the release of all NH 4 (super +) initially within the zeolite structure. A modified AMAS technique is proposed for measuring the CEC of zeolitic material.