Three lipopeptides derived from HBV-S (139–148) sequence containing stearoyl, cholanoyl, and Pam3-Cys(Ser)2 moieties were studied as far as their interactions with phospholipids are concerned. The parent compound and the three analogues have surface activity and penetrate lipid monolayers composed of DPPC. The miscibility of these peptides with the same phospholipid was nearly ideal. The area molecule values calculated for the parent peptide suggest an α-helical structure and the predicted secondary structure for this sequence, determined by the Chou and Fasman parameters, is also consistent with this conformation. The lipophilic derivatives show, nevertheless, higher molecular areas that fit better with an α-helix and β-sheet segments linked by a β-turn. The Pam3Cys(Ser)2 derivative showed an anomalous behavior both in HPLC and in monolayer experiments, probably the bulkiness of the hydrophobic moiety gives preferentially a micellar structure.