In this study, several Primaquine diphosphate (PQ) liposomal formulations containing phospholipid, charge inducer and with or without cholesterol in molar ratios of 7:1:(2) and 10:1:(4) were investigated. Gel state (DPPC:CHEMS:CHOL and PL-100H:CHEMS:CHOL) and liquid-crystalline state (PL-100:CHEMS:CHOL and PL-90G:CHEMS:CHOL) liposomes were prepared. The film method followed by sonication and extrusion through polycarbonate membrane was used. Particle size distribution, percentage of entrapped active substance, content of phospholipid and bilayer type and composition were determined. Lamellarity was determined by P-31-NMR technique. In vitro release of PQ was investigated at 37 degrees C, 35 rpm and in Tris (pH: 7.4) buffer. In vitro release and its fit to kinetic models were investigated. Liposomes were labelled by Tc-99m and injected intravenously to Swiss Albino mice.