With the use of a variety of techniques, pulmonary function was evaluated for a period up to two years following reimplantation of the left lung in six dogs which had no gross abnormality of the reimplanted lung by autopsy. The Hering-Breuer and cough reflexes were not present in the reimplanted lung. Xenon-133 studies measured an average of 39 percent of the total aerated volume, 40 percent of the total air exchange, and 34 percent of the total blood flow in the reimplanted left lung. Differential bronchospirometry with oxygen uptake demonstrated 39 percent of the total tidal volume and 33 percent of the total blood flow in the left lung. A close correlation was observed between pulmonary function measurements by both techniques. No significant deterioration or improvement in function was found by xenon-133 studies for a period of up to two years following lung reimplantation. A lower Po2 arterial blood occurred with induced unilateral hypoxia of the nonoperated lung than with the reimplanted lung. In three dogs studied ten months after reimplantation, marked bronchoconstriction of the left lung occurred with vagal stimulation, thereby confirming functional reinervation of the reimplanted lungs. © 1973.