Critical reagents are essential components of immunoassays that are used throughout the drug discovery and development process.  Reproducible assay performance is highly dependent upon the stability and consistency of critical reagents, which can include proteins, antibodies, and antigens.  Critical reagents are commonly conjugated to fluorescent molecules, colored reagents, or enzymes to quantify the assay reaction, or they are conjugated to solid surfaces, such as microtiter plates or beads, to enhance assay processing and workflow.  These various modifications can significantly impact reagent and assay performance; therefore, it is imperative to characterize critical reagent modifications and track their stability.  Radix has been performing critical reagent conjugations for years and has an active research program focused on improving the conjugation process, developing conjugation chemistry alternatives, and enhancing the reagent characterization process.  Each Radix conjugate is supplied with a certificate of analysis that can be included in a critical reagent management program.