This paper proposes a new, fast and precise method to analyze isoniazid based on the electrochemical oxidation of the analyte at a glassy carbon electrode in 0.1M NaOH. The quantification was performed utilizing amperometry associated with batch injection analysis (BIA) technique. Fast sequential analysis (60determinationsh −1 ) in an unusually wide linear dynamic range (from 2.5×10 −8 to 1.0×10 −3 M), with high sensitivity and low limits of detection (4.1×10 −9 M) and quantification (1.4×10 −8 M), was achieved. Such characteristics allied to a good repeatability of the current responses (relative standard deviation of 0.79% for 30 measurements), were explored for the specific determination of isoniazid in isoniazid–rifampin tablet.