The retention of various metal ions by water-soluble poly(4-vinylpylidine) methyl iodide in conjunction with ultrafiltration membrane was investigated. The method is based on the retention of inorganic ions by this polymer in a membrane filtration cell and subsequent separation of low-molecular weight species from the polymer metal ion complex formed. It is shown that the polychelatogen can bind silver(I) and mercury(II) ions in aqueous solution at pH 1. At higher pH, the water-soluble polymer can be applied to the separation and preconcentration of silver metal ions. Therefore, this polychelatogen is highly selective to Hg(II) at pH 1 with respect to metal ions such as Cd(II) and Zn(II).