Nitrates of one iosmeric form of the chloro-n-propylamine- and chloroisopropylamine-bis(ethylenediamine)-cobalt(III) cations have been prepared and characterised. They are assigned a cis-configuration on the basis of infrared observations. The first-order rate constants for the solvolytic aquation of these cations have been determined at different temperatures and the Arrhenius parameters calculated. These results have been discussed in terms of a unimolecular rearrangement between the solvation shell and the co-ordination shell of the complex. The second-order rate constants for the hydrolysis by base of these cations have also been determined at 0° and ionic strength 0·1M. These results are consistent with an S_N1/P mechanism.