The electroreductive behavior of cefdinir was investigated and two irreversible well-defined cathodic peaks were observed. From the electrochemical response the main reduction steps were found to be related to the reduction of C = N and C = C group. A fully validated, sensitive, and reproducible squarewave cathodic adsorptive stripping voltammetric procedure for the trace determination of the bulk drug, pharmaceutical formulation and in human urine, at the mercury electrode has been developed. The optimal experimental parameters for the drug assay were: accumulation potential -0.3 V (vs Ag/AgCl, 3 M KCl), accumulation time 15 s, frequency = 120 Hz, pulse amplitude = 0.07 V, and scan increment = 10 mV in phosphate buffer pH 2. The first peak current showed a linear dependence with the drug concentration over the range 1.88x10(-6) to 12x10(-8) M. The achieved limit of detection and limit of quantification were 0.5x10(-9) M (0.2 ng mL(-1)) and 1.7x10(-9) M (0.67 ng mL(-1)), respectively. The procedure was applied to the assay of the drug in capsule form with mean percentage recoveries of 99.7. Applicability to assay the drug in urine samples was illustrated. The peak current was linear, with the drug concentration in the range 0.08-0.7 mu g mL(-1) of the urine. (c) 2007 The Electrochemical Society.