Scatter plots of (A) plasma Cu concentration and (B) Cp activity of rats fed diets differing in Zn and Cu. Each solid circle corresponds to one rat (n = 12/diet group). The horizontal line across all diet groups represents the non-response mean of Zn-30 rats and that of the non-responders from other diet groups (see Methods). The dashed line within each diet group signifies the response mean for that diet group. The non-response mean (diet group Zn-30) and the response means (diet groups Zn-60, Zn-120, Zn-240 and Cu-D) were compared. Diet groups without a common letter differ (P < 0.05).