The secondary structure of P2 protein, isolated from bovine peripheral nervous system myelin, in reconstituted myelin was studied using Fourier transform infrared (FTIR) spectroscopy. Spectra of the protein in aqueous solution and in the lipid environment were compared and notable changes were observed. It was proposed that there are significant differences in the conformation of the protein in the contrasting environments. An increase in alpha-helical structure was observed for the protein in myelin and the significant amount of beta-structure observed in aqueous solution was reduced. The degree of alpha-helix appears to be related to the neuritogenic activity of the P2 protein. The findings of this study also support the view that the presence of both alpha-helices and beta-structure plays a significant role in membrane proteins.