The Lung Cancer Study Group (LCSG) has tested the efficacy of intrapleural bacillus Calmette-Guérin (BCG) as surgical adjuvant treatment in a double-blind, randomized comparison against intrapleural saline. This clinical trial included specific anatomic and pathological staging requirements and careful follow-up monitoring. At this time, with a median follow-up of 516 days in 216 treated and 209 control patients, no evidence has yet been found that postoperative instillation of intrapleural BCG improves survival or extends the disease-free interval in patients with completely resected Stage I squamous cell carcinoma, adenocarcinoma, or large cell carcinoma of the lung. There have been 93 recurrences and 77 deaths, which are remarkably evenly distributed in both arms of the study. An unexpectedly superior survival rate for the Stage I group has been observed, and the prognostic importance of cell type, TN status, and elevations in initial white cell count and alkaline phosphatase measurement has been confirmed.