Ni(II) and Cd(II) ions contained in aq. soins. of their sulfates were sepd. by permeation through polymer inclusion membranes contg. di(2,4,4-trimethylpentyl)phosphinic acid (CYANEX 272) as a mobile carrier. The permeation rate equations were derived taking into account the aq. film diffusion of metal ions and the membrane diffusion of metal-CYANEX 272 complexes. The mass transfer coeffs. of both metal ions and metal-CYANEX 272 complexes were also detd. in the permeation cell. The calcd. permeation rates agreed well with exptl. data.