Ovarian non-Hodgkin's lymphomas (NHLs) are rare, and accurate diagnosis is frequently problematic. Previous studies have not provided either complete immunotypic or genotypic analyses. The authors report immunotyping and genotyping of three cases of ovarian NHL, including both primary and secondary types. Immunotyping disclosed all three were B-cell lymphomas composed of secretory blast stage lymphocytes showing kappa immunoglobulin (Ig) light chain clonal excess. DNA extracted from frozen tissue of each tumor was subjected to restriction endonuclease digestion and hybridized to probes for Ig genes, C kappa, C lambda, JH, and the T-cell receptor beta-chain gene. Rearrangements of the heavy chain and light chain Ig genes were observed in all three cases, confirming the monoclonal B-cell origin of the neoplastic population. No detectable rearrangements were observed in DNA extracted from three nonlymphoid ovarian tumors (dysgerminoma, granulosa cell tumor, and fibrothecoma). This study documents the potential value of immunotyping and genotypic analysis in the study of ovarian tumors.