Artificial spheres consisting of concentric phospholipid bilayers encapsulating an aqueous PBS (phosphate buffered saline) solution containing clodronate. Liposomes are particles, sized at a max. of 3 micron. They are forming a suspension in PBS and will tend to precipitate upon storage, forming a pellet on the bottom of the tube or flask. The suspension should be shaken before administration to laboratory animals in order to recover the homogeneous suspension.