Adsorptive stripping voltammetry was used for the determination of trace amounts of theophylline. Theophylline in pH 7.5 Britton-Robinson buffer gives an adsorptive stripping voltammetric peak at a hanging mercury drop electrode at –0.38 V at accumulation potential 0.0 V versus Ag—AgCl. The optimum conditions of pH, accumulation potential and accumulation time were studied using differential-pulse voltammetry. The calibration graph for the determination of theophylline was linear in the range 0.6–3.6 µg l^–1 with a relative standard deviation of 2%. The detection limit was 0.6 µg l^–1 after 180 s accumulation at 0.0 V. The effect of some purine compounds and metal ions on the peak height of theophylline was studied. The presence of Cu^II ions enhanced the theophylline peak and the behaviour of the theophylline–copper complex was investigated. The method was applied to the determination of the drug in commercially available dosage forms. A comparison of the proposed method with previously reported methods was also made.