Possible activation of a volume receptor mechanism was studied using intermittent positive-pressure breathing (IPPB) with an end-expiratory airway pressure of zero. Urine formation, plasma antidiuretic hormone (ADH) levels, respiratory airway mechanics, cardiac output and cardiovascular function were measured during spontaneous ventilation and IPPB in dogs anesthetized with chloralose. Minimal changes in respiratory mechanics and cardiovascular function were observed. However, in all instances, urinary output increased and plasma levels of ADH decreased during mechanical ventilation. Upon resumption of spontaneous respiration, urinary output and plasma ADH returned toward control levels. Therefore, IPPB is not the direct cause of water retention through the activation of a volume receptor mechanism and the release of antidiuretic hormone.