Voltammetric studies have been carried out on 6-mercaptopurine (6MP) deposited at a silver electrode. 6MP yields a cathodic stripping signal at about -1.0 V (vs. Ag/AgCl) in pH 7.2 sodium phosphate buffer. Under selected conditions a linear calibration plot was obtained over the range of 0.2-6 mM with a relative standard derivation of 2.9 % for 1 mM 6MP (n ¼ 11, t d ¼ 60 s). The voltammetric response of 6MP was dependent on experimental conditions such as solution pH and potential-scan range. Generally 6MP exhibits two adjacent peaks in acidic solutions (pH < 6, C < 0.1 mM), a sharp peak in pH 6-9 solutions, and a broad wave with a small peak in basic solutions (pH > 9). Cetyltrimethylammonium bromide causes an enhancement of the cathodic stripping peak.