Abstract Excised leaves of Avicennia marina (Forsk.) Vierh. secreted chloride at rates of up to 3.5 μmol m −2s −1 when their petioles stood in concentrated solutions of sodium chloride. Maximum secretion rates occurred when the leaves were exposed to 1.0 M sodium chloride, and minimum rates when they were exposed to dilute (<0.10 M) or very concentrated (>2.0 M) solutions. The maximum rate of Cl − secretion from excised leaves was about an order of magnitude greater than that commonly found for intact leaves on mangroves under field conditions. Over the first 24 h, the leaves maintained an approximate salt balance by secreting as much Cl − as they took up in the transpiration stream over NaCl concentrations of 0.10–2.0 M. When excised leaves were exposed to 1.0 M solutions of NaCl, KCl or MgCl 2, the cation they secreted was mainly that comprising the treatment solution. In contrast, when they were exposed to 0.01 M solutions of NaCl, KCl or MgCl 2, they secreted mainly Na +, and very little K + or Mg ++.