This study compares the red blood cell (Rbc) levels of lead (Pb), calcium (Ca), and magnesium (Mg) in relation to blood pressure in 39 pregnant women in the third trimester of pregnancy. The study population included 20 women with normal pregnancies, 15 with mild hypertension, and 4 with severe hypertension and preeclampsia. The mean +/- SD for each group was calculated and the difference between the means of the normotensive and the other groups were compared by analysis of variance. Significant differences from normal to the preeclamptic pregnancies were in (1) elevated Rbc Pb (p < or = 0.001), (2) lower Rbc Ca (p < or = 0.001), and (3) lower Rbc Mg/Pb ratio (p < or = 0.0001). Pearson's rank correlation between blood pressure showed a direct relation to the Rbc Pb level (p < or = 0.01) and an inverse relation to the Rbc Ca and Mg/Pb ratio (p < or = 0.004, < or = 0.007). Apparently, prenatal blood pressure is directly proportional to Rbc Pb content and related or modified by Rbc Ca and Mg.