We examined the characterization of the antiviral T lymphocytes elicited by immunization with a novel liposome vaccine (MDP‐virosome) constructed with synthetic muramyldipeptide:[6‐0‐(2‐tetradecylhexadecanoyl)‐N‐acetylmuramyl‐L‐alanyl‐D‐isoglutamine], cholesterol, influenza virus haemagglutinin and neuraminidase. The haemagglutinin glycoprotein first appeared to induce a significant subtypespecific cytotoxic activity through its arrangement on the inner and outer surfaces of the MDP‐virosome. Splenocytes of BALB/c mice immunized with the virosome vaccine containing H3 haemagglutinin and N2 neuraminidase from human Hong Kong virus markedly lysed H3N2 virusinfected target cells, but not those infected with virus possessing a different subtype such as H1N1 surface antigens. Exposure of these splenic lymphocytes to virus antigenin vitrofurther enhanced their cytotoxic activity. The cytotoxic lymphocytes generated by the MDP‐virosome vaccine expressed Thy 1 and CD4 antigens on their cell surface, and these activities were restricted by class II histocompatibility gene products. The marked reduction of pulmonary virus litres in infected mice caused by transferred immune spleen cells suggested that the MDP‐virosome vaccination is able to protect against influenza virus infection through enhanced