The relationship between ceruloplasmin, a metalloenzyme with oxidase activity, and copper was investigated in Frisian dairy cows.The oxidase activity of ceruloplasmin correlated closely with the serum copper concentrations in Frisian dairy cows. Variations of copper (Cu) concentration and ceruloplasmin (Cp) activity in serum of dairy cows at different stages of lactation were assessed in 60 Frisian dairy cows. Furthermore, ceruloplasmin to copper ratios were also investigated. The cows were classified according to their lactation stages into three different groups as early lactation stage (4–6 weeks postpartum), mid-lactation stage (17–22 weeks postpartum) and late-lactation stage (25-30 weeks post-partum). Each group consisted of 20 multiparous cows. Serum samples were obtained from each cow for estimation of cereloplasmin activity and copper levels. Concentrations of serum copper (sCu) were higher in the group of early lactation stage than the other groups (P < 0.05). Serum cereloplasmin (sCp) activity also showed significant difference between early lactation, mid and late lactation groups (P < 0.05). The ratios of cereloplasmin activity to copper concentration (Cp/Cu) were significantly changed in the different lactation stages of dairy cows (P< 0.05). For evaluation of copper status, use of sCp/sCu identified more animals as ‘low' and ‘marginal'. It can be concluded that ceruloplasmin and copper undergo a physiological increase justafter calving; thus, their values should be interpreted with caution during assessment of copper status. Further research is required to refine diagnosis criteria for use of such ratio in determining copper status in Frisian dairy cows.