The electric potential, copper ion flux, and ammonia flux across the interface of cuprammonium cellulose solution (CCS) and various 1.0 equiv/L electrolyte solutions (ES) at 25OC were measured. The interfacial potentials were strongly negative (-10 to -35 mV) with H2S04, HCl, and (NH4)$04 as ES, weakly positive (6 to 8 mV) with NaCl, KCl, LiCI, CsCL, and RbCl as ES, and strongly positive (19 to 34 mV) with KOH and NaOH as ES, generally showing values similar to the diffusion potentials for electrolyte solutions comprising ions of the same absolute charge. The ammonia flux (about 1 X mol/cm2/s) was relatively unaffected by the interfacial potential, but the copper ion flux was clearly dependent on it. These results, together with the observed rates of CCS coagulation, indicate that the mechanism of the coagulation was largely determined by the interfacial potential, with strongly negative potential gradients accelerating the Cu2+ flux into the ES and CCS coagulation proceeding rapidly by Cuz+ removal, strongly positive potential gradients ac - celerating the Na' flux into the CCS and coagulation proceeding rapidly via the formation of cellulose-Na+ complex, and the absence of a strong potential gradient capable of acce1.erating the ion flux resulting in slow coagulation by ammonia removal. It may therefore be possible to control the interfacial potential and the ion flux by the ES composition, and thus to influence the structure of regenerated cellulosic fibers and membranes.