The voltammetric behavior of isradipine was studied using direct current (DC(t)), differential-pulse (DPP) and alternating current (AC(t)) polarography. Isradipine exhibited well-defined cathodic waves over the whole pH range in Britton-Robinson buffer (BRb). At pH 5, the analytical pH, the diffusion-current constant (Id) was 8.27+/-0.52. The current-concentration plots were rectilinear over the range 1-20 and 0.1-18 microg/ml using the DC(t) and DPP modes, respectively, with minimum detectability of 0.01 microg/ml (2.7 x 10(-8) M) using the latter technique. The current has been characterized as being diffusion-controlled, although adsorption phenomenon played a limited role in the electrode process. The proposed method was applied to commercial tablets and capsules. The percentage recoveries were in good agreement with those given by the manufacturer. The method was further extended to the in-vitro determination of the drug in spiked human urine and plasma, the percentage recoveries were (n = 4) 100.12+/-1.42 and 103.88+/-5.13, respectively. The number of electrons involved in the reduction process was accomplished and a proposal of the electrode reaction was presented.