Liposomes composed of the lipids of biological membranes are suitable for drug delivery. To reach a better therapeutical effect it is important to know the properties of interactions between the drug and lipid molecules. From dipalmitoyl phosphatidylcholine (DPPC) using ultrasound small liposomes containing morphine were prepared. The amount of entrapped morphine was determined with spectrophotometry and luminescence spectroscopy. The interaction between the molecules of morphine and its derivates (codeine, N-methyl-morphine, N-methyl-codeine) and the DPPC lipid was studied with differential scanning calorimetry (DSC) and electron spin resonance (ESR) methods. Our studies indicated that the molecules of morphine and its derivates principally interact with the environment of DPPC lipid head groups. Due to the interaction the mobility of head groups decreases especially in case of codeine and N-methylcodeine.