In this study we evaluated the effect of penetrating anion size on the properties of the channels formed by cyclic lipodepsipeptide syringomycin E (SRE) in bilayer lipid membranes. Conductance and the mean lifetime of the SRE channels have been measured in 0.4 M solutions of sodium chloride, aspartate, and gluconate. Comparison of the results of conductometrical and electrophysiological measurements has shown: 1) ratio of mobilities of aspartate anions in the channel and in the water solution is 5 times lower than that for chlorine anions; 2) conductivity of the channels in the presence of sodium gluconate is due mainly to cations. The results obtained indicate binding of the penetrating anions to the selective filter of the SRE pore. The radius of the SRE channel selective filter has been established (r - 0.3 nm) and its localization in the cis-mouth of the pore has been found.