Risk factors for early pulmonary complications occurring within the first 3 months after autologous bone marrow transplantation (BMT) were analysed in 158 consecutive adults. The long-term effects of autologous BMT on pulmonary function were analysed in 102 patients, who had survived free of disease for > 6 months after autologous BMT. Pulmonary function tests were performed before, at 6 and 12 months after autologous BMT and thereafter annually. The median follow-up was 12 (6-60) months. The incidence of early pulmonary complications was 16% (26 of 158). Idiopathic interstitial pneumonitis was seen in 11% of patients treated with total body irradiation (TBI). Single dose TBI was the major risk factor as regards early pulmonary complications but restrictive pulmonary disturbances and impaired diffusing capacity prior to autologous BMT were also significant risk factors. In both non-TBI and TBI-treated patients a mild restrictive ventilatory dysfunction and impaired diffusing capacity was noted 6 months after autologous BMT. In non-TBI-treated patients, these disturbances had resolved completely within 2 years whereas the lung volumes of TBI-treated patients were persistently reduced by 10% of their pre-autologous BMT values during follow-up. However, dysfunctions rarely progressed 6 months after autologous BMT. In most patients, ventilatory dysfunction was slight and had no clinical significance.