Methylan polysaccharide was aminated to add dialkylaminoethyl and free amino groups at hydroxyl sites in the methylan backbone, and these derivatives were quaternized to produce pH-independent cationic polyelectrolytes. The immunological activities of the resulting methylan derivatives were investigated. Diethylaminoethyl (DEAE)-methylan derivatives inhibited the classical pathway of the complement system in a dose-dependent way. Quatemized DEAE-methylan exhibited the highest anticomplementary activities among the all derivatives. Anticomplementary activities increased significantly as the cationic charge of the methylan derivatives increased via aminoderivatization followed by quaternization, indicating that there is an electrostatic interaction between the methylan derivatives and the negatively charged functional residues on the cell.