Spirometry and krypton-81m lung scans were performed in 17 patients before lobectomy was carried out for bronchogenic carcinoma to determine whether post-operative spirometric values could have been predicted from the pre-operative data. The patients were followed up at 3, 6 and 12 months post-operatively for lung function testing. It emerged from this study that good post-operative spirometric values could be predicted for VC (r = 0.80), and for FEV1 (r = 0.88), and to a much lesser degree for the TLC (r = 0.51) at 6 months after surgery. With time TLC and VC tended to increase, whilst the FEV1 remained at the same level.