al. Abbott Prism: a multichannel heterogeneous chemilumines-

sitivity and signal amplification than did the three-step assay. Under the three-step conditions, only limited amounts of the biotinylated antigen could be available to form complexes with acridinium-labeled anti-biotin. On the other hand, with the use of preformed complex, the opti-mum binding of biotin to anti-biotin could have occurred in solution. Interestingly, this precomplex has shown good stability when stored at 2-8 #{176}Cfor 6 months. We have therefore incorporated the technique in the current Prism HCV assay. In summary, the use of precomplex eliminates the separate steps of antigen and antibody addition, increas-ing the time- and cost-effectiveness of the method. More-over, the use of a precomplex appears to enhance Prism HCV assay sensitivity