Target-sensitive (TG-S) liposomes having modified antibodies on their surface were employed to study the release of calcein and the selective delivery of the anticancer agents, doxorubicin(DOX) and methotrexate (MTX). The release of calcein from TG-S liposome occurred when the various target cells were contacted with liposomes and it was proportionally increased with the increase of antibody affinity to the target cells. Increasing the concentration of antigen molecules (major histocompatibility, MHC) on the surface of RMA-S, the release of calcein and drugs from TG-S liposomes was only induced above a threshold density of surface antigen on the target cell membrane. The growth inhibition of specific target cells by the liposomal drugs was always stronger than that of the non-specific ones. For specific target cells, the IC₅₀ of liposomal DOX was about 2 times greater than that of free DOX, on the while, for non-specific target cells, more than 5 times. This indicates that the liposomal drugs were transferred preferentially to the specific target cells than the non-specific ones. Based on this phenomenon, the TG-S liposomal MTX were also applied for the selective elimination of the specific target cells in the mixed culture of specific and non-specific target cells.