PHARMACOLOGICAL studies on diacylphospholipids develop along two lines of investigation. In the first, preparations of liposomes are used as carriers of drugs either bound to the bilayer or entrapped inside the vesicles. Sonicated liposomes have been shown to be able to transport inhibitors or drugs to target sites in vitro1 and in vivo2. In the second, liposome preparations are administered and pharmacological effects are recorded. In this context significant effects have been observed on cholesterol distribution5. The molecular mechanism underlying the possibility of pharmacological effects in vivo by long chain diacylphospholipids is indicated by a series of investigations4–7 showing the capacity of phospholipid vesicles to fuse with cellular membrane in vitro. As a consequence of changed composition of membrane lipids, alteration in the permeability properties, transport systems and other functions of biological membranes are expected to occur. It has been shown8 that sonicated dispersion of bovine brain phospholipids can induce in mice modification of glucose distribution. Purification of lipid mixtures indicated that phosphatidylserine was one of the active components. Phosphatidylserine liposomes have shown great capability to interact in vitro with biologically active compounds (histamine9 or calcium10), with phospholipid-dependent enzymatic systems (Na+–K+-stimulated ATPase11 or tyrosine hydroxylase12), or with intact cells (enhancement of histamine release during antigen–antibody interaction13; promotion of cell fusion4). In this investigation data on phosphatidylserine-induced effects in vivo are presented.