With the goal of identifying genes with a differential pattern of expression between ovarian serous papillary carcinomas (OSPCs) and normal ovarian (NOVA) epithelium and using this knowledge for the development of novel diagnostic and therapeutic markers for ovarian cancer, we used oligonucleotide microarrays with probe sets complementary to 12,533 genes to analyze the gene expression profiles of 10 primary OSPC cell lines, 2 established OSPC cell lines (UCI-101, UCI-107) and 5 primary NOVA epithelial cultures. Unsupervised analysis of gene expression data identified 129 and 170 genes that exhibited >5-fold upregulation and downregulation, respectively, in primary OSPC compared to NOVA. Genes overexpressed in established OSPC cell lines had little correlation with those overexpressed in primary OSPC, highlighting the divergence of gene expression that occurs as a result of long-term in vitro growth. Hierarchical clustering of the expression data readily distinguished normal tissue from primary OSPC. Laminin, claudin 3, claudin 4, tumor-associated calcium signal transducers 1 and 2 (TROP-1/Ep-CAM, TROP-2), ladinin 1, S100A2, SERPIN2 (PAI-2), CD24, lipocalin 2, osteopontin, kallikrein 6 (protease M), kallikrein 10, matriptase (TADG-15) and stratifin were among the most highly overexpressed genes in OSPC compared to NOVA. Downregulated genes in OSPC included transforming growth factor-beta receptor III, platelet-derived growth factor receptor alpha, SEMACAP3, ras homolog gene family member I (ARHI), thrombospondin 2 and disabled-2/differentially expressed in ovarian carcinoma 2 (Dab2/DOC2). Differential expression of some of these genes, including claudin 3, claudin 4, TROP-1 and CD24, was validated by quantitative RT-PCR and flow cytometry on primary OSPC and NOVA. Immunohistochemical staining of formalin-fixed, paraffin-embedded tumor specimens from which primary OSPC cultures were derived further confirmed differential expression of CD24 and TROP-1/Ep-CAM markers on OSPC vs. NOVA. These results, obtained with highly purified primary cultures of ovarian cancer, highlight important molecular features of OSPC and may provide a foundation for the development of new type-specific therapies against this disease.