Selected cations (Ca, Co, Cu, Mg, Zn, Si, and K) were determined in the placentae of 18 women. Between pre-eclamptic and normal subjects there were significant (p less than 0.05) differences in copper and zinc concentrations and borderline significant differences in cobalt concentration. In the placentae of the ten women with a normal pregnancy, the average concentrations of copper and zinc were 53 and 192 micrograms atoms/kg placenta, respectively. In the placentae of 8 women with pre-eclampsia, the concentrations were 124 and 134 micrograms atoms/kg placenta for copper and zinc, respectively. Elevation of copper and decrease in zinc may be an exaggeration of normal pregnancy physiology that occurs in pre-eclampsia.