The levels of zinc in plasma, erythrocytes, polymorphonuclear (PMN) and mononuclear (MN) white cells were measured after delivery in women giving birth to appropriate-for-gestational-age (AGA) babies (group I mothers), or small-for-gestational-age (SGA) babies (group II mothers) and in non-pregnant controls. Mean maternal plasma zinc and albumin levels 24-48 h after delivery were lower than in controls, but PMN and MN zinc levels were unchanged. PMN zinc levels were lower than those of MN cells. PMN and MN zinc levels were significantly lower in group II mothers than in group I, irrespective of smoking habits. There were no racial differences in peripheral white cell zinc levels. PMN, and to a lesser degree MN, zinc levels were lower in smoking than in non-smoking mothers. Erythrocyte zinc did not correlate with other zinc measurements nor with the size of the babies. Fetal erythrocyte zinc levels were one-third of maternal levels. A combination of smoking and/or low PMN zinc levels selects 85% of mothers having small-for-gestational-age babies.