The SSX genes are members of the family of cancer/testis antigens that encode tumor-associated antigens recognizable by autologous cytolytic T lymphocytes. Their expression is common in tumors of diverse lineages and absent in normal tissues except testis and thyroid. In this study, sixty-seven neuroblastomas (NB) (12 stage 1, 13 stage 2, 12 stage 3, 12 stage 4S and 13 stage 4) were examined by RT-PCR and a sensitive chemiluminescent detection method for SSX-2 and SSX-4 expression. Seventy-two percent (13/18) of stage 4 NB expressed SSX-2 and 67% (12/18) expressed SSX-4. SSX-2 and SSX-4 positivity correlated with metastatic NB stage 4 (p=0.02 and p=0.006, respectively). Sensitivity experiments showed SSX-2 detection was one tumor cell in 10(6) normal cells, and one in 10(4) for SSX-4. All normal tissues (n=6), with the exception of testis, normal bone marrow (BM, n=12) and normal peripheral blood (PBL, n=10) were negative for SSX-2 and SSX-4 expression. Thirty-two BM and 14 PBL obtained from 35 stage 4 NB patients at 24 months from their diagnosis were evaluated for SSX-2 expression. Unlike another cancer/testis antigen, GAGE, only one BM sample was positive, and no prognostic utility could be established. Further investigation of SSX expression at other relevant time points is warranted.