The relative usefulness of various indices of (ir) reversibility in predicting survival is reported for 129 patients with severe chronic airflow limitation (initial Forced Expiratory Volume in one second, FEV1, less than or equal to 1000 ml). The generally applied increase of FEV1 as a percentage of the initial FEV1 value (delta FEV1% in) and the increase of FEV1 as a percentage of the predicted FEV1 after an anticholinergic drug (delta FEV1%pred) are not related to survival. The increase of FEV1 as a percentage of the "maximal" attainable increase to the predicted level, as estimated by predicted minus initial FEV1 (delta FEV1%(predin], is, next to the severity of airflow obstruction after bronchodilation (FEV1pb% pred), significantly related to prognosis. After controlling for smoking, delta FEV1% (pred-in) was the best indicator of reversibility in prognosis prediction. Next to smoking and delta FEV1% (pred-in) also the irreversible part of airflow obstruction FEV1%FIV1 after bronchodilation appeared to influence survival independently in this particular patient population with severe airflow obstruction.