In this paper, the electrochemical behavior of luminol in weakly acidic solution was studied. It is found that Co2+ remarkably enhances the electrochemiluminescence (ECL) of luminol in citric acid-sodium citrate buffer solution (pH = 4.0) when a pulse potential (-1.8 to + 1.0V, versus Ag/AgCl) is applied to the Pt electrode. The selectivity for Co2+ is very good because most of the other water-soluble metal ions do not interfere. A sensitive and selective ECL method for determination of Co2+ is proposed. After optimization of the reaction conditions and electrochemical parameters influencing the relative ECL intensity, the linear range responding to Co2+ is 5.0 x 10(-12) to 1.0 x 10(-7) mol/L, and the detection limit is 2.0 x 10(-12) mol/L. The relative standard deviation for 5.0 x 10(-10) mol/L cobalt(II) is 3.7% (n = 11). © 2004 Elsevier Ltd. All rights reserved.