A series of isatin derivatives containing an adenine or theophylline fragment have been synthesized. The corresponding N '-[2-(trimethylammonio)acetyl] and N '-(2-pyridinioacetyl) hydrazones have been found to exhibit neither cytotoxicity nor hemotoxicity. Quaternary salts based on adenine derivatives of 5-methyl- and 5-ethylisatins showed the highest antiplatelet activity which exceeded the activity of acetylsalicylic acid by a factor of 1.5.