The experimental behaviour under linear sweep and cyclic voltammetry at low scan rates of the reduction of pb(2+) and Cd2+ at solid and mercury microelectrodes is reported in the presence and in the absence of supporting electrolyte. The major effects observed on decreasing the concentration of supporting electrolyte are an increase in the steady-state limiting current and more drawn out curves during the direct scan, broader and asymmetric stripping peaks on the reverse scan. These effects are rationalized in terms of the contributions of migration associated with diffusion in the mass transport and ohmic polarization which adds to concentration polarization when the concentration of supporting electrolyte is decreased. The experimental results are also compared with theoretical predictions.