Enhanced ultrafiltration by the addition of polymers soluble in water is a promising technique for the recuperation of heavy metals in wastewater streams. In this work an analysis is made of the influence of the molecular weight (inferior and superior to the molecular weight of the polymer) cut-off of the membrane and the quantity. of the polymer on the permeate flux and the recovery of mercury. The results show that with a membrane with a cut-off inferior to that of the combination metal polymer, the polymer concentration has no influence on the permeate flux, whereas for the membrane with a superior cut-off, there appears restrictions to the passing of water in accordance with the hydrodynamic model, and there is decreased efficiency in the recuperation of metal.