The Cu(II), Ni(II), Co(II) and Zn(II) catalysed dissociation of the cis-diaquobis(malonato)chromate(III) ion has been studied kinetically in perchloric acid solution over a temperature range. Under these conditions kobs = kH[H+] + Kcat [M2+] where kobs is the observed first order rate constants and kH and Kcat are the appropriate rate constants for the proton and metal ion catalysed pathways respectively. The metal ion exert marked catalytic effects with kcat following the sequence Cu(II) > Ni(II) > Co(II) > Zn(II). A possible mechanism for the metal promoted reaction is proposed and the relevance of these results to the mechanism of the trans → cis isomerisation of [Cr(mal)2 (H2O)2]- considered. © 1981 Gordon and Breach Science Publishers, Inc.