The potential of liposomes to act as immunoadjuvant carriers of tumor-associated antigens (TAA) has been investigated. The incorporation of B16 melanoma TAA within liposomes resulted in immunological recognition by non-tumor-bearing mice, and subsequent inhibition of tumor growth upon tumor challenge. The immunogenicity and protective activity were enhanced by the concomitant incorporation of a lipophilic immunoadjuvant, MDP-GDP, in the liposome preparation. The ability of liposomal preparations to augment the immunogenicity of a human oncofetal antigen, CEA, was also studied. The incorporation of CEA within liposomal carriers resulted in immunological recognition in mice at doses (0.1 micrograms) significantly less than required in Freund's complete adjuvant (25 micrograms), maximal responsiveness being found with liposomal-CEA-MDP-GDP preparations. Liposomal TAA vaccines may therefore require the presence of immuno-adjuvant-active agents for the induction of effective immunological responses in individuals at risk from recurrent disease.