The nm123-H1 gene has been proposed as a metastasis suppressor gene. It is located on the long arm of chromosome 17, which is frequently deleted in ovarian cancer, and shows altered expression and structure in some advanced neoplasms. To evaluate the role of nm23-H1 in ovarian carcinogenesis, we have analyzed this gene in 66 primary human ovarian carcinomas at both the DNA and RNA levels. Despite the high frequency (76%) of nm23-H1 loss of heterozygosity (LOH), the complete absence of gene mutations in the coding portions of the retained allele clearly indicated that, in ovarian carcinomas, this gene does not function in the same way as do classic oncosuppressor genes. The relationship of clinicopathological parameters with nm23-H1 gene deletions and expression levels was also investigated. LOHs were more common in the serous and endometrioid histotypes (85 and 93%, respectively), and the highest LOH frequency was detected in poorly differentiated tumors (89%). A significant relationship between nm23-H1 mRNA expression and lymph node metastasis was observed in high-grade tumors, which are intrinsically more invasive than are low-grade tumors. In particular, among the poorly differentiated tumors showing areas of undifferentiated solid carcinoma (classified as G(3)/G(4)), lymph node-negative tumors displayed expression levels that were significantly higher than those of lymph node-positive tumors (P < 0.001). In conclusion, our data suggest that the nm23-H1 gene product may exert an inhibitory effect on the lymphatic dissemination of human ovarian tumors. However, several other factors, biological or time and patient dependent, influence the complex metastatic progression of ovarian tumors and may cooperate with nm23-H1 in the promotion or inhibition of this process.