The objective of this study was to analyze the diagnostic and clinical role of the folate receptor-alpha (FOLR1) and folate receptor-gamma (FOLR3) genes in effusion cytology. Expression of the FOLR1 protein product, FR-alpha, was additionally studied. Ninety-one effusions (71 ovarian carcinomas, 10 breast carcinomas, 10 malignant mesotheliomas) were assayed for FOLR1 and FOLR3 gene expression using quantitative polymerase chain reaction. FR-alpha expression was analyzed using flow cytometry. Ovarian carcinoma expression levels were analyzed for association with clinicopathologic parameters and survival. Quantitative polymerase chain reaction analysis showed significantly higher FOLR1and FOLR3 mRNA levels in ovarian carcinomas compared with both breast carcinomas and mesotheliomas (P < .001). FOLR1 and FOLR3 mRNA levels were directly interrelated in ovarian carcinoma (P < .001). FR-alpha protein levels were similarly higher in ovarian carcinoma compared with the 2 other cancer types (P < .001). FOLR1and FOLR3 mRNA and FR-alpha protein expression in ovarian carcinoma effusions showed no association with clinical parameters or survival. Our data suggest that folate receptor levels effectively differentiate ovarian carcinoma from other cancers affecting the serosal cavities and that folate receptor genes are coexpressed in this tumor. The high expression of folate receptors in ovarian carcinoma supports their validity as molecular therapeutic targets in this disease.