BELGARD EV (BELEV) and BELGARD EV 2000 (BELEV 2) are polymeric formulations used as anti-scale agents in MSF distillers. BELEV results from the self-polymerization of maleic anhydride while BELEV 2 is a terpolymer of the same monomer. The two agents lack analytical procedures for controlling their active constituents. We found that Cd2+, Pb2+ or Hg2+ ions react with the two agents in hexamine buffer of pH 6 to produce gelatinous precipitates of definite composition. The relations between the amounts of cations bound to BELEV (BELEV 2) (m. equiv.-) and the quantities of the agents (mg) are linear, passing through the origin. The results obtained allow the calculation of the equivalent weights of unit cells bound to the cations. For BELEV these amount to 220, 166 and 158 for Cd2+, Pb2+ and Hg2+, respectively. The most probable structure of the formed precipitates are suggested. For BELEV 2 the corresponding figures are 310, 265 and 255, successively. The feasibility of estimating the active constituents of BELEV and BELEV 2 in their preparation is highlighted.