The interfacial behavior of antifungal lipopetides of the iturinic group was studied in comparison with that of surfactin, an anionic lipopeptide. All these lipopeptides were isolated from various strains ofBacillus subtilis; each strain produced surfactin and one antifungal compound. The iturinic compounds differ from surfactin by their lower surfactant properties. The critical micelle concentration (CMC) values were dependent on the nature of the peptide moiety in the iturinic compounds. The highest values were observed for anionic antibiotics. The arrangement of lipopeptides at the air-water interface was largely dependent on the size of the lipid moiety; surfactin, which has a C14or C15β-hydroxy fatty acid, iturins A, C, and bacillomycins D, L, which have a C14or C15β-amino fatty acid, occupied a smaller area than mycosubtilin and bacillomycin F, which have a C16or C17β-amino fatty acid. These data can be related to bioactivity of these lipopeptid