Reverse transcriptase (RT)-PCR with primers specific for surfactant protein A (SP-A), B (SP-B), C (SP-C), and D (SP-D) genes was applied to detect metastatic non-small cell lung carcinomas. Forty-one paratracheal and subcarinal lymph nodes obtained from 41 patients with non-small cell lung carcinomas, 11 lymph nodes from 11 patients with extrapulmonary adenocarcinomas, and eight control lymph nodes from patients without cancer were analyzed using RT-PCR. PCR products corresponding to SP-B gene products were found in all eight control lymph nodes, offering evidence of SP-B gene expression in cells of lymphatic tissue. SP-A, SP-C, and/or SP-D transcripts were detected in 11 (84.6%) of 13 lymph nodes with histologically identifiable metastases of pulmonary adenocarcinomas and in 10 (55.5%) of 18 lymph nodes that were tumor free on routine histological examination. These findings provide evidence of micrometastatic nodal involvement which remains undetectable by conventional light microscopy but can be evaluated by surfactant RT-PCR. Gene expression of SP-A and SP-C was restricted to metastatic pulmonary adenocarcinomas but SP-D gene activity has been also detected in two of four metastases of pulmonary large cell carcinomas, one adenosquamous carcinoma, and nine extrapulmonary adenocarcinomas as well.