hSNF5/INI1 is one of the components of the SWI/SNF multiprotein complex that is necessary for the transcriptional activation of several genes and functions by altering chromatin structure. This gene has been thought to be one of the tumor suppressor genes (TSGs) because deletions or mutations were reported in malignant rhabdoid tumors and atypical teratoid and rhabdoid tumors. To evaluate the hSNF5/INI1 gene as a TSG in lymphoid malignancies, we performed a mutational analysis in 23 patients with non-Hodgkin lymphoma (NHL), 24 with acute lymphoblastic leukemia (ALL), 24 with multiple myeloma (MM), 24 with adult T-cell lymphoma/leukemia (ATLL), and 19 with lymphoid cell lines, by polymerase chain reaction-single-strand conformational polymorphism (PCR-SSCP) analysis. Nonsense and missense mutations were found in 1 NHL case and 2 cell lines. Mutations from this NHL case proved to be somatic in origin. These data indicated that alterations in the hSNF5/INI1 gene might be involved in the pathogenesis of lymphoid malignancies.