The reduction mechanism of a series of nickel(11) dithiocarbamates has been investigated in dimethyl sulphoxide at the mercury electrode. Under controlled-potential conditions, the reduction proceeds initially by an ECE mechanism (electron transfer-chemical reaction-electron transfer) with n = 1 for both electron transfers. The chemical reaction involves a dissociation to produce a nickel species more easily reduced than the nickel(11) dithiocarbamate. However, for some derivatives, rate constants for the chemical step show a time dependence, at electrolysis times above 5 s, consistent with an ECCE mechanism of the type where the product of the first chemical reaction reacts further to produce a nickel species more difficult to reduce than nickel(11) dithiocarbamate. Exhaustive reduction of nickel(11) diethyldithiocarbamate at the mercury-pool electrode gave non-integral n-values (2 > n > 1) consistent with the ECCE mechanism, and demonstrated that the product of the second chemical reaction is reoxidized to nickel(11) diethyldithiocarbamate by oxygen. The nature of the complete electrode reaction suggests a metal-centred reduction.