Liposomal and free rifabutin were separated by the method of gel filtration. The percents of rifabutin bound to liposomes of different phospholipid composition were measured. The presence of negatively charged phospholipids increased the degree of binding. Binding decreased with increasing the ionic strength. Incubation of rifabutin with liposomes containing anthryl phosphatidylcholine was accompanied by fluorescence quenching. Activity of rifabutin depended on the phospholipid composition of liposomes. Our results indicate that binding of rifabutin is associated with electrostatic and hydrophobic interactions.