We describe a novel class of light-triggerable liposomes prepared from a photo-polymerizable phospholipid DC(8,9)PC (1,2- bis (tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine) and DPPC (1,2-Dipalmitoyl-sn-Glycero-3-Phosphocholine). Exposure to UV (254 nm) radiation for 0-45 minutes at 25 degrees C resulted in photo-polymerization of DC(8,9)PC in these liposomes and the release of an encapsulated fluorescent dye (calcein). Kinetics and extents of calcein release correlated with mol% of DC(8,9)PC in the liposomes. Photopolymerization and calcein release occurred only from DPPC/DC(8,9)PC but not from Egg PC/DC(8,9)PC liposomes. Our data indicate that phase separation and packing of polymerizable lipids in the liposome bilayer are major determinants of photo-activation and triggered contents release.