18 bronchogenic carcinomas (16 adenocarcinomas, one squamous cell carcinoma, and one large cell carcinoma) in 17 patients and the control group (benign nodules) were examined with high resolution and thin section CT. Thin-section CT images showed airbronchogram or airbronchiologram in 63%, multiple small cavitations in 63%, and heterogeneous densities 50% of the adenocarcinomas with excellent spatial and contrast resolution. Airbronchogram or airbronchiologram was not seen in other types of bronchogenic carcinomas and benign nodules. Therefore, demonstration of airbronchogram or airbronchiologram in nodular lesions can make the CT diagnosis of small peripheral bronchogenic carcinomas, especially adenocarcinomas.