We propose to use novel Palladium Catalyzed Chemical Amplification (PdCCA) technology to develop ultra-sensitive bioassays that can detect very low concentrations of tumor biomarkers in blood. PdCCA is a generic technology that can be universally applied to different assay platforms. In the bioassay application considered here it uses a detection antibody labeled with a palladium catalyst and a subsequent, palladium catalyzed, high gain redox reaction generating a water-soluble formazan dye. PdCCA will be adapted to the standard ELISA format, where it may provide a factor of 102 to 103 fold increase in sensitivity in immunoassays for which a detection antibody of high selectivity is available. This increase in sensitivity will lower the detection threshold of currently used methods to the desired range of ng-pg/ml, allowing for development of screening biomarkers for early tumor detection. Phase I of the proposed work will concentrate on technology development and optimization using a set of three biomarkers for ovarian cancer and, optionally, one biomarker of breast cancer, currently under study at the Fred Hutchinson Cancer Research Center, Seattle, WA (FHCRC). We will optimize the dye forming amplification chemistry and spectrophotometric detection, and use model in vitro assays to develop and optimize the bioassay technology. Feasibility of our approach will be demonstrated on clinical specimens stored at the FHCRC.