Prior attempts at in vivo reversible vagal denervation of the gastrointestinal tract have been limited to cervical cooling techniques that also denervate both sympathetic and vagal pulmonary and cardiac branches. Denervation of vagal efferent fibers at this level has produced results that are inconsistent with those obtained after surgical truncal vagotomy. We have, therefore, developed a technique to provide reversible vagal denervation below the pulmonary and cardiac branches for the study of gastric motility. Five dogs, previously equipped with gastric strain gages and electrodes, underwent implantation of a tubular cooling jacket around a distal thoracic vagal trunk with contralateral vagotomy (4 dogs), or around both vagal trunks (1 dog). The jacket was made of stainless steel tubing in a "J" design. Its inside channel was lined with a sterling silver sheet, and a thermistor was attached to record temperature change. Silicone tubing coursed externally to a pump and flask to which 95% ethanol at -70 degrees C was circulated at variable speeds. Thoracic vagal cooling, extending up to 5 h, reversibly blocked gastric contractions induced by insulin hypoglycemia. Contractile waves were terminated at device temperatures of 2 degrees-6 degrees C but promptly returned with warming. Dogs were tranquil during denervation, and enclosed nerves remained functional for greater than 40 days.