The effect of the anticancer drug 6-mercaptopurine (6-MP) on mineral metabolism was investigated in mice. C57Bl/6J female mice were injected intraperitoneally with 6-MP at 100 mg/kg body wt for one, two, four, or five consecutive days. On d 6 of the study, liver, kidney, and intestine were removed, and concentrations of zinc, copper, iron, manganese, magnesium, and calcium were measured. Hepatic concentrations of zinc, copper, iron, and calcium became higher as the number of drug injections increased. To determine if the altered mineral metabolism was a function of a drug-induced, acute-phase response, liver metallothionein and plasma ceruloplasmin were measured. Metallothionein concentrations in the liver became higher with increased number of injections, correlating with the stepwise increase in hepatic zinc. Gel filtration chromatography showed that most of the increase in liver zinc concentration was associated with a protein of mol wt of 6000-8000, the approximate weight of metallothionein. Ceruloplasmin concentrations were not affected by 6-MP injection. These results suggested that 6-MP alters zinc metabolism by sequestering zinc into the liver via induction of metallothionein synthesis and that the drug may induce an acute-phase response with an atypical acute-phase protein profile.