A cytologic examination of pleural fluid was performed on a pleural lavage specimen collected at the completion of operation after pulmonary resection in 135 of 599 patients undergoing curative pulmonary resection for a non-small cell carcinoma of the lung between 1977 and 1982. The cytologic results of lavage was positive for malignant cells in 12 of the 135 patients (8.9%). The incidence of positive results was correlated with lymph node status (N2 greater than N1 greater than N0), cell type (adenocarcinoma greater than other non-small cell lung cancers), stage (III greater than II greater than I), and visceral pleural status (invaded greater than not invaded). No positive cytologic results were noted in 39 patients having a diagnostic excisional pulmonary biopsy prior to more definitive resection. The disease has recurred in nine of the 12 patients with positive cytologic results (only two in the ipsilateral pleural space), and eight have died. The prognostic role of pleural lavage cytology needs more study.