Sensitive cathodic stripping voltammetric procedures for trace determination of xanthine (I), 7-methylxanthine (II) and 1,7-dimethylxanthine (III) are reported. The methods are based on the accumulation of the copper(I) complexes of the compounds on the hanging mercury drop electrode. The adsorptive stripping response was evaluated with respect to accumulation time, potential, concentration, pH and other variables. Linear calibration graphs were obtained over the range from 2.0 × 10⁻⁸ to 2.0 × 10⁻⁹ M; the limits of detection, with accumulation times of 4 min for I and III, and of 6 min for II, were calculated to be 5.0 × l0⁻¹⁰ 1.0 × 10⁻⁹ and 5 × 10⁻¹⁰ M, respectively. Possible interferences by other purine derivatives were examined. The simultaneous determination of 1.7-dimethylxanthine (paraxanthine) and theophylline is possible by the proposed method.