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Freeze-fracture electron microscopy, quasi-elastic light scattering and 31P solid-state NMR have been utilized in order to follow morphological changes of melittin-dipalmitoylphosphatidylcholine complexes as a function of temperature. For lipid-to-protein molar ratios greater than 10 and up to 30, a reversible transition occurs, from discoidal structures of diameter N 100 to 400 A, at low temperature, to vesicular structures of diameter N 30~~~ A, at high temperature. This transition appears to be triggered by the phospholipid acyl chain melting. Higher concentrations of me&tin (e.g. lipid-to-protein ratio of 5.2) prevent this morphological transition, i.e. small complexes of N 100-250 A diameter remain stable throughout the temperature range. Melittin Phosphohpid membrane Disc-to-vesicle transition Chain melting Quasi-elastic fight scattering NMRFreeze-fracture