The feasibility and the good immediate acceptability of unilateral lung transplants in the patients with obstructive respiratory problems have recently been demonstrated and since the initial reports, some hundreds of lung transplants have been performed in various parts of the world for this indication. Nevertheless, few results of respiratory function are currently available in the medium term. We report these in a series of 20 patients with severe obstruction who were given single lung transplants. The actual probability of survival for 1 and 2 years was 75 and 70% respectively with 4 peri-operative deaths and 2 later deaths. In the 16 survivors of more than 6 months, in relation to the pre-operative values, a significant improvement was observed 3 months after the graft in the FEV1 which rose from 17 +/- 6 to 53 +/- 13% of the predicted values. The PaO2 rose from 52 +/- 10 to 81 +/- 3 mmHg. The distance covered on the six minute walking test went from 99 +/- 84 m before the graft to 587 +/- 147 m 6 months after the operation. In addition to the improved distance, the lung function was stable in a group of patients as the months went by, although there was a fall in the respiratory function in others with the appearance of the syndrome of bronchiolitis obliterans or in 2 patients with bronchial complications. The four patients with severe deterioration in the graft function were re-transplanted with a good clinical result in three of them, the fourth dying in the immediate post-operative period. We conclude that single lung transplant represents an effective treatment both in the short and medium term in patients with chronic airflow obstruction.