The invention provides a screening method and screening kit for a cell protecting agent. Specifically, the invention provides a method for screening a cell protecting agent showing an Hsp90-binding activity and a heat shock protein expression-inducing activity but having no Hsp90 client protein degradation-promoting activity. The method comprises the following steps (1) to (3): (1) measuring the binding property of a test compound to Hsp90 (2) measuring the activity of a test compound to induce the expression of a heat shock protein, or measuring the activity of a test compound to disrupt an Hsp90/HSF-1 complex, by using a cell capable of expressing the heat shock protein and (3) measuring the activity of a test compound to induce the degradation of an Hsp90 client protein by using a cell capable of expressing the Hsp90 client protein. The invention further provides specifically a kit for screening a cell protecting agent, comprising (1) Hsp90 (2) a reagent for measuring the heat shock protein expression-inducing activity (3) an imidazothiazine derivative and (4) a reagent for quantifying an Hsp90 client protein.
