Because caffeine and tissue levels of Zn are closely related, the objectives of this study were to determine the changes in plasma caffeine levels over a period of 5 h when different concentrations of Zn combined with a fixed concentration of caffeine were injected into the femoral vein of rats and to determine the relationship between tissue levels of caffeine and Zn at 5 h postinjection. Rats were divided into three groups: group 1, 220 microg caffeine; group 2, 220 microg caffeine + 8 microg Zn/g body weight (BW); group 3, 220 microg caffeine + 16 microg Zn/g BW. Blood from groups 1 and 3 was collected at 3 min, 30 min, 1 h, 3 h, and 5 h to determine the pharmacokinetics of caffeine. All groups were killed at 5 h. Caffeine and Zn concentrations of the brain, kidney, heart, and liver of all groups were determined. The plasma-caffeine curve in group 3 showed a lower concentration at 3 min and a slower caffeine-elimination rate during the first 3 h. Brain and kidney caffeine levels remained constant in all groups, whereas caffeine levels were increased in the heart in group 2 and in the liver in group 3. Zn concentrations in the brain and kidney were lower in group 2 compared with groups 1 and 3 and higher in group 3 compared to groups 1 and 2. Zn concentration in the heart was the same among the three groups but was increased in the liver in group 3 compared to groups 1 and 2. Therefore, we concluded that caffeine combined with Zn affects caffeine pharmacokinetics. With caffeine intake, levels of Zn (16 microg/g BW) that are slightly higher than the daily requirements (12 microg/g BW) may prevent a reduction of Zn in tissue. In addition, caffeine's effects on Zn concentration among organs are different.