Platelet-derived growth factor (PDGF) is synthesized and secreted by mesenchymal cells. We used immunohistochemistry and in situ hybridization to determine whether immunoreactivity for PDGF and PDGF receptor (PDGF-R) might be a prognostic indicator in lung carcinoma. We compared these results with those of immunohistochemistry for anti-proliferating cell nuclear antigen (anti-PCNA). Indirect immunohistochemistry and in situ hybridization were performed for PDGF B-chain, PDGF-R beta and PCNA antibodies, and PDGF B mRNA on frozen, paraffin-embedded sections of 92 surgically resected lung carcinomas (39 squamous cell carcinomas, 47 adenocarcinomas, 2 large-cell carcinomas, 2 adenosquamous carcinomas, and 2 double carcinomas). Clinicopathologic data (sex, age, stage, survival period, histologic type, and degree of cell differentiation) were evaluated using a statistical analysis system. PDGF reactivity was positive in tumor cell cytoplasm in some cases of squamous cell carcinoma (64%) and adenocarcinoma (55%) and in all cases of large-cell carcinoma, adenosquamous carcinoma, and double carcinoma. PDGF-R reactivity was detected only in tumor stroma. Positive PDGF staining was associated with a poor prognosis in patients with lung carcinoma, independent of age, sex, stage, and degree of cell differentiation (risk ratio = 2.53, p = 0.03). PDGF B mRNA was detected in 100% of PDGF-positive squamous cell carcinomas and in 85% of adenocarcinomas. There was no correlation between PDGF expression and PCNA index in lung carcinomas. Together, these results suggest that immunohistochemistry for PDGF B-chain may predict the outcome for lung carcinoma patients.