Ninety-two patients with histologically confirmed bronchogenic carcinoma treated by surgical resection of the tumour were subsequently given immunotherapy with BCG (Glaxo). The patients were randomly allocated into three groups. Twenty-nine patients received multipuncture BCG (50 to 250 X 10(6) viable units), and twenty-six patients intradermal BCG (0.4 to 0.9 X 10(6) viable units), treatment being given at 1, 2, 6, 9, 13, 26, and 52 weeks after operation. Thirty-seven control patients did not receive any BCG immunotherapy; two patients in the control group were lost to follow-up. The overall five-year survival in all groups was 37%. Favourable prognostic features were squamous carcinoma (45% five-year survival), the absence of involved mediastinal nodes at operation (46%), and lobectomy (45%), but even the presence of involved mediastinal nodes was associated with a 19% five-year survival. There were no statistically significant differences between the survival of the control group and either group treated by immunotherapy considered individually or in combination. The influence of the presence of positive mediastinal lymph nodes and the extent of surgical resection on survival was not affected by immunotherapy. No serious side-effects of immunotherapy were encountered.