An equation is derived for the current in staircase voltammetry at any sampling time at a microdisk electrode for a reversible electrode reaction. On the basis of this equation, three differential staircase voltammetries are developed for the reversible case. Differential current equations of three methods have been derived for the same potential step and different time sampling current (SPDT), different potential step and same time sampling current (DPST), and different potential step and different time sampling current (DPDT) respectively. Experimental results for the oxidation of K-4[Fe(CN)(6)] in the presence of KCl at platinum ultramicrodisk electrodes were found to agree with theoretical predictions. The data obtained also demonstrate that the differential staircase voltammetry for DPDT is the most sensitive of the three methods.