NY-ESO-1 mRNA expression was investigated in advanced prostate cancer by conventional and quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR). NY-ESO-1 mRNA was detected in 20 of 53 (38%) tumor specimens. Four of 15 (27%) stage C, 1 of 3 stage D1 (33%) and 15 of 35 (43%) stage D2 prostate cancers were positive. The presence of NY-ESO-1 antibodies was evaluated in sera from a panel of 218 patients with prostate cancer, including the 53 patients whose tumors were examined for NY-ESO-1 mRNA expression. NY-ESO-1 antibodies were detected in 1 of 30 (3.3%) stage D1 and 9 of 110 (8.2%) stage D2 patients, whereas none of the 78 patients with localized prostate cancer (stages A, B and C) had detectable NY-ESO-1 antibodies. Of the 53 patients whose tumors were examined for NY-ESO-1 mRNA expression, 2 of 20 patients with NY-ESO-1 mRNA-positive tumors had NY-ESO-1 antibodies. No antibody was found in the sera of 32 patients with NY-ESO-1 mRNA-negative tumors, with the exception of one patient with regional lymph node metastasis (stage D1). CD8 T cell responses specific to NY-ESO-1 were detected in two of three patients with NY-ESO-1 antibodies.