Second-harmonic alternating-current voltammetry can be used for the sequential determination of two electroactive species having very similar half-wave potentials (deltaE(1 2 ) < 50 mV). Since the concentrations of such metals in samples of special interest are often at trace levels, for their determination second-harmonic a.c. voltammetry (extremely selective but not sufficiently sensitive) can usefully be combined with the anodic stripping method, which has a very high analytical sensitivity. The determination of tin and lead as well as of indium and cadmium in 1M hydrochloric acid is described. The half-wave potentials are only 35 and 45 mV apart, respectively, for these systems. A three-electrode cell was used with a long-lasting sessile-drop mercury electrode as the working electrode, with a drop-time of 240-300 sec. The detection limit was found to be 10(-8)M for all four elements studied. The precision expressed as the relative standard deviation was 2-3% and the relative error was 1-2%.