Bacteriologic cultures of sputum and specimens obtained at thoracotomy from 17 patients with cystic fibrosis were compared. All organisms found in the surgical specimens were found in the sputum. Only two surgical specimens failed to yield any organisms. The most frequently isolated organisms were Pseudomonas aeruginosa (41%) and Pseudomonas cepacia (35%). Serotypes of P. aeruginosa and antibiogram results on both P. aeruginosa and P. cepacia further supported the concordance of the isolates from the two sources. In addition, anaerobic cultures were obtained in specimens from 10 patients with CF and revealed two patients with anaerobic colonization of the lower respiratory tract. These findings also correlated well with the sputum cultures. The correlation of sputum and lung specimen culture results supports the value of sputum culture in the management of lung disease in CF.