STEAP was identified by the strategy of suppression subtractive hybridizations in Los Angeles prostate cancer xenografts. It is expressed in prostate and other cancers, and not in most normal tissue; it can be used as a marker to evaluate biological samples from individuals suspected of having a disease associated with STEAP dysregulation, such as cancers, and may provide prognostic information useful in defining appropriate therapeutic options. The aim of this study was to test the STEAP mRNA detection in the serum of patients with different malignant tumours by using Real-Time reverse transcription PCR. The results were compared with biological samples obtained by age-matched non-malignant donors. Our data demonstrated that STEAP mRNA is detectable in serum of patients with different solid tumours whereas it is not amplifiable in non-malignant donors. This marker revealed with the molecular method of quantitative PCR in serum, may be useful to discriminate normal and cancer patients.