['To determine whether the use of autologous blood clot seal (ABCS) after biopsy of lung lesions can reduce or prevent pneumothorax.', 'The authors evaluated 100 patients (63 men, 37 women; age range, 27-78 years) with pleural (n = 23) or deep (n = 77) lesions. Thirty-eight patients had emphysema. Patients were randomly assigned to one of two groups: those in whom the biopsy track was sealed with autologous blood clot (n = 50) and those who did not receive autologous blood clot (n = 50). Biopsy was performed with computed tomographic (CT) guidance and a 19-gauge coaxial system. The autologous blood clot, which ranged from 0.5 to 4.5 mL, was injected while the sheath was being withdrawn.', 'Pneumothorax developed in four of the 23 patients (17%) with pleural lesions and 19 of the 77 patients (24%) with deep lesions. Pneumothorax occurred in four of the 45 patients (9%) who had deep lesions and received autologous blood clot and in 15 of the 32 patients (47%) who had deep lesions and did not receive autologous blood clot (P <.001). In patients with emphysema, pneumothorax occurred in three of the 20 patients (15%) who received autologous blood clot and 10 of the 14 (71%) who did not (P <.001). There were seven large pneumothoraces necessitating treatment; all occurred in patients who did not receive autologous blood clot.'] Do autologous blood clot seal to prevent pneumothorax at CT-guided lung biopsy?