1. This study investigated the effects of supplemental copper and chromium on the serum and egg traits of laying hens using 144 forty-five-week-old White Leghorn layers. The hens were randomly assigned into 9 groups to conduct this 3 copper (0, 125 and 250 mg/kg as copper sulphate) x 3 chromium (0, 800 and 1600 microg/kg as chromium picolinate) factorial trial. 2. Egg yolk cholesterol was significantly reduced by supplementary copper (Cu) and chromium (Cr) and there was an interaction between Cu and Cr supplementation. Egg production, egg weight, eggshell strength and eggshell thickness were not influenced by Cu or Cr supplementation. 3. Serum cholesterol concentration was decreased by Cu supplementation and very low-density lipoprotein (VLDL) was reduced markedly by both Cu and Cr. On the other hand, high-density lipoprotein (HDL) was significantly increased by Cu and Cr. Interaction occurred between Cu and Cr in the VLDL and HDL parameters. Supplmentary Cu also reduced VLDL-cholesterol (VLDL-C) and enhanced HDL-cholesterol (HDL-C), while supplemental Cr had a contrary effect on these two parameters. 4. If minimum egg cholesterol content is the criterion, this study suggests that 125 mg/kg of Cu together with 800 to 1600 microg/kg of Cr provide adequate supplementary concentrations for laying hens.