To evaluate the usefulness of fiberoptic bronchoscopy for treatment of acute lobar atelectasis, 31 subjects were randomly allocated to fiberoptic bronchoscopy followed by respiratory therapy for 48 hours, or to respiratory therapy alone for the same period. No significant differences between groups with regard to restoration of volume loss were detected after the first treatment intervention, at 24 or at 48 hours (P greater than 0.20). Specifically, the mean percentage resolution of volume loss immediately after bronchoscopy (38 per cent) closely approximated that after the first respiratory therapy treatment in subjects who had not undergone bronchoscopy (37 per cent). An air bronchogram proved to be a predictor of delayed resolution for both groups. At 24 hours, 26 per cent of the air bronchograms demonstrated 83 per cent resolution (P less than 0.001). These results suggest that fiberoptic bronchoscopy does not add to respiratory therapy in the treatment of acute lobar atelectasis and that an air bronchogram predicts delayed resolution of collapse.