A simple extractive spectrophotometric method has been described for the determination of metribuzin herbicide. Metribuzin was reacted with copper and a stable complex in the presence of ammonia (0.2 M) at pH 10.5 was formed. The resulting yellow coloured complex was extracted in chloroform and showed absorption maxima at 340 nm. Beer's law was obeyed in the range of 0.8-25 mu g mL(-1) with molar absorptivity of 5.67 x 10(3) L mol(-1) cm(-1). The composition of the complex was studied by Job's method of continuous variation and the results indicated that the mole ratio of metribuzin:Cu2+ is 2:1. The optimum reaction conditions for complexation and other analytical parameters were evaluated. A two-level factorial design was also used to determine the effect of different parameters and their interaction on metribuzin:Cu2+ complex formed. The method was successfully applied for the determination of metribuzin in commercial formulations and real samples. (C) 2008 Elsevier B.V. All rights reserved.