|With publications discussing deficiencies in steroid immunoassays, including radioactive analyses, LC-MS/MS is becoming a noted alternative technique. Here we present a comparison of LC-MS/MS and immunoassay for the analysis of testosterone. The mass spectrometric assay was performed on an AB SCIEX API 5000¢â LC-MS/MS system interfaced with a Shimazu Prominence HPLC system, using a one-step liquid-liquid extraction without derivatization. The LOD of the assay was ¡Â5pg/mL at S/N ¡Ã5. The immunoassay for testosterone was performed on a Siemens (DPC) Immulite 2000. The assay is a solid-phase, competitive chemiluminescent enzyme immunoassay. A strong correlation was observed between the two techniques.