The effect of 6-mercaptopurine (6-MP) on mineral metabolism was investigated in mice. C57BL mice were given 6-MP for 5 consecutive days. Treatments were: no injection; saline; vehicle injection (carboxymethylcellulose (CMC]; 5 mg/kg 6-MP; 25 mg/kg 6-MP; 50 mg/kg 6-MP; 100 mg/kg 6-MP; and 150 mg/kg 6-MP. After the 5-day period, tissues were removed and the levels of calcium (Ca), magnesium (Mg), zinc (Zn), copper (Cn) and manganese (Mn) were measured. In liver, but not in intestine or kidney, zinc and calcium levels increased in a dose-dependent manner. The weight of the stomach relative to body weight was significantly greater in mice receiving 100 mg/kg and 150 mg/kg BW doses of 6-MP than in those given lower doses, despite significantly lower body weight. This result indicated that 6-MP produced gastric toxicity. Injection of saline or vehicle had no effect on any of the parameters measured. The effect of 6-MP on mineral changes and on stomach-emptying may be partly responsible for at least some of its negative side-effects.