This paper addresses itself to the question of whether it is possible to calculate the postoperative values for cardiopulmonary function before surgery, Data of 29 patients were analyzed before and 6 months after pneumonectomy: whole body plethysmography, ergometry, blood gas analysis, right heart catheterization, and quantified perfusion scan of the lung. Using a simple formula, the postoperative value was calculated preoperatively and compared with the value actually measured 6 months postoperatively. The results showed a fairly good correlation for lung volumes, especially FEV1 (r = 0.66; P < 0.001), but no good predictability for the pulmonary hemodynamics (e.g., Pap = 38.6 +/- 9.8 mmHg preoperatively calculated vs. 29.9 +/- 6.3 mmHg postoperatively measured). These results and the predominant prognostic value of FEV1 are the basis of a suggested flow sheet for preoperative evaluation of patients undergoing pneumonectomy.