The theory for the technique of a.c. differential pulse polarography is presented. Since the waveform is a linear combination of d.c. differential pulse polarography and sinusoidal a.c. polarography the possibility of obtaining a wide range of electroanalytical responses at different time domains is considered. Advantages in analytical and kinetic investigations are discussed. Experimental data for reduction of cadmium in 1 M NaCl and zinc in 1 M KCl (pH 3.0) are presented. For the latter system the drop time and temperature dependence reveal anomalous behaviour showing the model of a quasi-reversible electrode process is inadequate.