To elucidate the effect of the peptide derived from cecropin A(1-8)-melittin(1-12) having potent antifungal activity without cytotoxicity against eukaryotic cell on the fungal cell membranes, Trichosporon beigelii protoplasts were prepared. The protoplasts treated with the peptide not only failed to regenerate the fungal cell walls but also disrupted the membrane, indicating that the peptide exerts its antifungal activity by acting on the plasma membranes.