Objective      To compare the difference between cell smear and cell block in differential diagnosis of pleural effusions

and to investigate the methods for differential diagnosis between lung adenocarcinoma and malignant mesothelioma.       Methods      Seventy-eight cases of pleural effusions were examined using cell smear and cell block

respectively. Cell morphology was observed by HE staining. Expression of CK7

MOC-31

CD15

BerEP4

CEA

TTF-1

CK5/6

calretinin

WT-1 and desmin were detected by SP immunohistochemical assay. The association of clinical and follow-up data with different cytology diagnostic methods was analyzed.       Results      The positive detection rate of the cell block was higher than that of the cell smear

but the positive detection rate by HE staining showed no significant difference between the two methods. The accordance rate of the cell block immunohistochemistry for the diagnosis of malignant pleural effusion was 46.2%

which was significantly higher than that of the cell smear (Chi-square=4.17

P0.01). CK7

MOC-31

CD15

BerEP4

CEA and TTF-1 were highly expressed in lung adenocarcinoma

whereas CK5/6

calretinin

WT-1 and desmin were highly expressed in malignant mesothelioma and mesothelial reactive hyperplasia.       Conclusion      Cell block has a certain diagnostic value for malignant pleural effusion

and its combination with immunohistochemistry and complex antibodies is helpful for the differential diagnosis between lung adenocarcinoma and malignant mesothelioma.