The Organoid Transparency Reagent and Three-Dimensional Tissue Staining Reagent are chemicals developed by the University of Tokyo and the RIKEN Institute with the aim of visualizing the detailed three-dimensional structures of organs and the entire body at high resolution in the context of basic drug discovery research and non-clinical research. These reagents are distinguished by their ability to observe tissues, which were previously only partially visible through 2D slices, in a three-dimensional manner with cellular-level resolution. They are among the safest and easiest-to-implement reagent kits globally, and they hold the potential to significantly enhance the efficiency of drug discovery research.