We report a part of a systematic investigation on the behaviour of lipopeptide analogues of myelin basic protein at the water-air interface. A palmitoyl moiety was introduced in different positions of a nonapeptide sequence of the human myelin basic protein. The lipopeptides, either alone or mixed with phospholipids, were studied at water-air interface by means of surface pressure-area and surface potential-area isotherms. The results deduced for the lipopeptide conformation at water-air interface were compared to the results obtained from the structural characterisation of Langmuir-Blodgett (LB) films of the above compounds. Information on the bidimensional miscibility of the lipopeptides with membrane phospholipids was deduced from the analysis of the experimental pi-A isotherms. These findings were correlated to clinical trials of the same substances and interpreted in terms of molecular interaction and lipopeptide conformation.