The results of studies on hemolytic and antioxidative activities of quaternary ammonium bromides and chlorides differing in alkyl chain length and with functionalized antioxidative group are presented. Pig erythrocytes (RBC) and their ghosts were used in experiments. The hemolytic studies permitted to determine the safe concentrations at which the compounds studied did not damaged RBC membranes. RBC were then UV-irradiated and the antioxidative efficiency of the quats determined. It was found that hemolytic activities increased with lipophilicity of a compound and each bromide salt was more hemolytic than chloride one. The antioxidant activity of the quats followed the same rule. The results obtained indicate that observed effects are the consequence of the incorporation of particular compounds to different depths into the lipid phase of the RBC membrane. The incorporation depended on lipophilicity of quats and the kind of counterions. The studies on fluidity changes induced by quats in ghost membranes confirmed above conclusion.