Polychlorinated biphenyls (PCB) are very toxic lipophilic substances widely used in the past as non flammable dielectric fluids. PCB accumulation in the environment appears to be a great risk for human health. Dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylethanolamine (DMPE) liposomes with increasing amounts of Aroclor 1254 have been studied by DSC and Raman spectroscopy.Noticeable changes take place in thermograms and Raman spectra even in the presence of small amounts of Aroclor, suggesting the existence of strong interactions due to the insertion of the PCB molecules into the hydrophobic core of liposomes.In DPPC liposomes, a 'solution like' system is observed and the main effects are the decrease of both the melting temperature and DeltaH of transition, with a simultaneous increase in the half width and asymmetry of the peak.On the contrary, in DMPE liposomes, a complex structure of the thermograms, which comes from the coexistence of different phases, is observed in most of the analysed systems. The behaviour is explained on the basis of a different penetration depth into the bilayer due to the polar interactions involving the polar head of the lipid.The existence of an interdigitate phase in DMPE-PCB liposomes is also evident in the experimental results. (C) 2003 Elsevier B.V. All rights reserved.