Isatin (indol-2,3-dione) is an endogenous indole, exhibiting various biological activities that are realized via its interacts with numerous target proteins (so-called isatin-binding proteins). To date, isatin-binding proteins have been characterized in the brain of mice and rats. In this study we have performed a comparative proteomic analysis of the isatin-binding proteins of the mouse liver and brain. Proteomic profiling of clarified lysates of membrane and soluble fractions of liver and brain homogenates was performed using 5-aminocaproyl-isatin as an affinity ligand. During affinity based separation of isatin-binding proteins of soluble and membrane fractions of mouse brain homogenates lysed with Triton X-100, 63 individual proteins were identified. A similar separation of mouse liver homogenate fractions during affinity chromatography resulted in identification of 80 proteins. All identified liver and brain proteins belonged to the following functional groups: (I) Carbohydrate metabolism and energy generation; (II) Lipid metabolism; (III) Metabolism of nucleotides and amino acids; (IV) Formation of the cytoskeleton, exocytosis; (V) Regulation of gene expression, cell division and differentiation; (VI) Antioxidant and protective proteins; (VII) Signal transmission and regulation of enzyme activity. The total number of isatin-binding proteins common for the brain and liver was only 12. The most common for the brain and liver of isatin-binding proteins was found in group VI (antioxidant and protective proteins), complete absence of coincidence in group II (lipid metabolism) and group IV (formation of the cytoskeleton, exocytosis). The observed differences in the profile of isatin-binding proteins appear to play an important role in the specific effects of isatin in certain organs.