The reactions of organic radicals, which are generated by pulse radiolysis in aqueous K2PtCl4 solutions containing an alcohol or ether, are trac:ed by optical absorption and conductivity methods. Upon attack by 1-hydroxyalkyl or 1-alkoxyalkyl radicals, PtCl42- disappears in a chain reaction, in which Cl- ligands are substituted by H2O. 2-Hydroxyalkyl radicals do not initiate the chain. The final product of attack by 1-hydroxyalkyl radicals is colloidal platinum.