We have developed a liposome formulation that, when exposed to gamma radiation, releases contents at a 10 fold higher rate than for non-irradiated liposomes. Liposomes composed of a non polymerizable matrix lipid and a polymerizable lipid having two sorbyl ester bearing fatty acid chains were found to leak only 6% of an encapsulated fluorescent dye after 1.5 hr at 37 C. When exposed to 20 or 50 Gy gamma radiation, these liposomes were found to release 70% or 90% of contents, respectively during the same time period. This enhanced leakage occurred in conjunction with a 20% to 30% loss of monomer, as measured by a decrease in absorbance at 250 nm.