Thirty-nine ventilation and perfusion lung studies with xenon 313 were perfomed in 29 patients with D-transposition of the great arteries (DTGA). Fifteen patients had simple DTGA and 14 more complex anatomic features. Inequalitiies of ventilation (V) were present in 23% (9/39) and perfusion (Q) in 44% (17/39) of studies. Six patients with simple DTGA showed abnormal distribution of perfusion, all with increased flow to the right lung. Among the 14 patients with complex DTGA, eight (57%) had abnormal distribution of perfusion. In patients with pulmonary artery band, increased flow was directed toward the left lung, and in those with an aorticopulmonary anastomosis, increased flow was to the side of the shunt. Radionuclide angiograms were performed in 17 patients with DTGA, both before and after surgical repair. In all, an abnormal circulatory pattern was noted. Complete superior vena cava obstruction present in four patients and residual left to right shunt (Qp/qs greater than 1.7/liter) in three was confirmed at cardiac catheterization. Ventilation perfusion studies with xenon-313 and technetium-99m radionuclide angiogram were effective noninvasive techniques in assessing pulmonary function and hemodynamics in patients with DTGA.