OBJECTIVE To study the function of c-myc and K-ras in tumorigenesis of ovarian cancer. METHODS K-ras and/or c-myc cDNAs were introduced into mouse ovarian surface epithelium cells (MOSE) using recombinant Moloney retroviral vectors. The resulting MOSE cells were studied by cell proliferation assays, the ability to form colonies in soft agarose, matrigel invasion assays and tumorigenicity assays in nude mice. RESULTS K-ras and c-myc can be easily delivered to the normal MOSE cells by recombinant retroviruses. mRNA and protein of the target genes can be detected by RT-PCR and Western blot. Cell proliferation assays showed that MOSE-Ras cells and MOSE-RM cells (MOSE-Ras/Myc) grew more rapidly than parental cells (MOSE) and MOSE-Myc cells (P <0.01). In addtition, MOSE-RM cells grew more rapidly than MOSE-Ras cells (P <0. 05). Cell colony formation assays showed that while MOSE-Ras and MOSE-RM cells can form colonies in soft-agarose, the MOSE-Myc and MOSE cells did not. Matrigel invasion assays showed that MOSE-Ras and MOSE-RM cells have invasion ability, but not MOSE-Myc ascites and the control MOSE cells. Xenograft experiments showed that MOSE-Ras and MOSE-RM cells were able to form tumors in nude mice following intraperitoneal injection. Tumors were not observed in animals injected with either MOSE-Myc or MOSE cells. CONCLUSIONS The recombinant Moloney retroviral system is a highly efficient and convenient method for introducing and expressing foreign genes in murine surface epithelial cell cultures. In this model, expression of K-ras alone is sufficient to generate tumorigenic MOSE, however expression of c-myc in conjunction with K-ras results in cells with a higher index of malignancy. Based on the assays described in this report, expression of c-myc alone can not transform MOSE cultures although it does play a role in cooperation with K-ras.