Abstract: A technique for the analysis of trace elements in serum is developed using proton-induced X-ray emission. The concentrations of K, Ca, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Br and Rb in serum of mice, normal and fed gossypol acetic acid, are determined. An obvious increase in the concentration of Cu and the decrease in the concentration of Zn of mice fed with gossypol acetic acid, as compared with those of normal mice, are observed, so that the Cu/Zn ratio of the former is significantly higher than the latter (P=0.05). No significant changes in the concentrations of K and Ca are observed, although the concentration of Ca of mice fed with gossypol acetic acid is lower.