In 15 normal mothers the stress effects of labor on zinc and copper distributions in erythrocytes and plasma were investigated. Lower levels of total zinc and of zinc derived from both carbonic anhydrase isoenzymes (CA-I and CA-II), especially from CA-I, in erythrocytes were obtained immediately after delivery. On the other hand, there was a significant increase in total plasma zinc concentration only on admission to hospital in labor, although albumin-bound zinc concentration remained elevated throughout the entire labor. These results suggest that there are unexplained disparities between the changes in zinc levels in maternal erythrocytes and plasma during labor.