The polarographic reduction of lead in the presence of selenite gives rise to an additional peak corresponding to the reduction of lead (Pb) on adsorbed selenium (Se) on mercury at - 0.33 V. The selenium and lead content can be determined using this peak by the addition of a known amount of one of these ions first and then the second ion. The linear domain range of lead is 5.0 x 10(-7)-2.0 x 10(-5) M and for selenium 5.0 x 10(-7)-1.0 x 10(-5) M. Using this method 4.90 x 10(-7) M Se(IV) and 1.47 x 10(-6) M Pb(II) in a synthetic sample could be determined with a relative error of + 2.0% and 1.8%, respectively (n = 4). A recovery test after acid digestion for a synthetic sample was 97% for selenium and 96.5% for lead. The method was applied to 1 mi of digested blood, and 328 +/- 23 mu g l(-1) Se(IV) and 850 +/- 62 mu g l(-1) Pb(II) could be determined with a 90% (n = 5) confidence interval. (C) 1998 Elsevier Science B.V. All rights reserved.