A novel family of amphiphilic temperature- and pH-sensitive poly(organophosphazenes) with varying ratios of ethylene oxide, alkyl chains and free acid units was synthesized by living cationic polymerization. Depending on their composition, these poly(organophosphazenes) exhibited lower critical solution temperatures ranging from 32 to 44 degreesC, which were pH-dependent for copolymers bearing carboxylic acid groups. The alkylated copolymers were then anchored into phospholipid bilayers to obtain stimuli-responsive liposomes that released their content upon a change in temperature or pH. Such polymer/vesicle complexes could find practical applications for site-specific and intracellular drug delivery.