An experimental study of a series of mercury microelectrodes, prepared onto a Pt disc substrate, with mercury thickness varying from almost a film to a shrouded sphere, is presented for cyclic voltammetry involving amalgam formation. The range of scan rates explored was between 5 and 200 mV s(-1), so that the dominant spherical diffusion, characteristic of the small electrodes, is affected to a different extent by planar diffusion depending on the scan rate employed. The cyclic voltammograms, taken from aqueous solutions containing test ions of Pb(II) and Cd(II) with different supporting electrolytes, showed that both mercury thickness and scan rates caused a shift toward less negative potentials of the cathodic-anodic pattern. A detailed analysis of the typical cyclic voltammetric parameters is done to characterize better the behaviour of these electrodes. An unusual trend has been observed for the current of the stripping peak as a function of the scan rate, the trend being either a monotone decrease or passing through a maximum depending on the thickness of the mercury deposit. The charge involved both in the cathodic and anodic scans and its dependence on scan rate and mercury thickness allowed to ascertain the occurrence of Pt-Cd intermetallic compounds. Similarities among the results here reported with other findings obtained at mercury micro and conventional film electrodes have also been discussed.