In a previous study dietary supplementation with 140 mg zinc (Zn) as Zn sulfate (ZnSO4) per day significantly decreased absorption of calcium (Ca) during a low Ca intake (230 mg/day) but not during a normal Ca intake (800 mg/day). The purpose of the present study was to determine whether smaller doses of Zn would also inhibit Ca absorption during the 230 mg Ca intake, and whether the 140 mg dose of Zn would inhibit Ca absorption during a Ca intake less than 800 mg/day. To investigate the first aspect, 100 mg Zn as ZnSO4, was given daily during a low Ca intake (230 mg/day) in six studies, and in the second phase, 140 mg Zn as ZnSO4 was given during a Ca intake of of 500 mg/day in five studies. Intestinal absorption of Ca was determined with tracer doses of 47CaCl2 in control studies and in the two Zn supplementation studies. Results showed that 100 mg Zn/day during a low Ca intake (230 mg/day) did not inhibit Ca absorption and that 140 mg Zn given during the 500 mg Ca intake also did not affect the absorption of Ca.