The interaction of B18 peptide with surfactants has been studied by circular dichroism spectroscopy and fluorescence measurements. B18 is the fusogenic motif of the fertilization sea urchin protein. The peptide forms an alpha-helix structure when interacting with positively or negatively charged surfactants below and above the critical micellar concentration (CMC). The alpha-helix formation is due to binding of surfactant monomers rather than the formation of surfactant micelles on the peptide. Fluorescence measurements show that the CMC of the negatively charged surfactant increases in the presence of B18, supporting the fact that there is a strong interaction between the peptide and monomers. Nonionic surfactant monomers have no effect on the peptide structure, whereas the micelles induce an alpha-helical conformation. In this case the helix stabilization results from the formation of surfactant micelles on the peptide.