Up to December 1973, we had performed 100 mediastinoscopies for lung carcinoma. Fifty-two were positive and 48 negative. In 80 cases there was clinical or radiological suspicion of mediastinal invasion. With radiological evidence of mediastinal node involvement exploration was positive in 32 out of 35 cases, when chest radiography findings were equivocal in 19 out of 45, and when radiology of the mediastinum was normal in only one of 20 cases. Mediastinoscopy was more frequently positive when the carcinoma was oat-cell or anaplastic. Of 48 patients with negative biopsies, 41 were explored. In 26 the carcinoma extended beyond the lung. In 1973 we circularized 83 thoracic surgeons concerning (1) the use of mediastinoscopy for patients with lung carcinoma assessed for surgery, (2) the significance of mediastinal node involvement, (3) the results of radiotherapy alone in patients rejected for surgery, and (4) the survival rate in patients with positive mediastinal nodes treated with surgery alone or together with radiotherapy. The replies to the questionnaire are summarized. The authors emphasize the usefulness of mediastinoscopy but state that care must be taken when deciding to withhold operation for a possible cure.