The mechanism of the base hydrolysis of the carbonato- and oxalato-bisethylenediaminecobalt III ions was investigated by measuring the rate of base hydrolysis spectrophotometrically under varying condi-tions. The steric changes accompanying the reaction was also followed by measurement of the change of optical activity during the reaction. In conjunction with this the rate of racemisation of the cis(-) 'dihydroxo-bisethylenediaminecobalt III ion was measured. . Mechan-istic paths are discussed.for comparative purposes the rate of base hydrolysis of the carbonatobis(1,10-phenanthroline)cobalt III ion was investigated. Further work using 1,10-phenanthroline as a ligand consisted of an investigation into the compounds formed between cobalt, chlorine and phenanthrol ine. The infrared spectra of the dichloro-, carbonato-oxalato-, malonato- and cyclobutane 1,1' dicarboxylate ob is-(1,10-phenanthroline)cobalt III complexes are recorded.