Raman spectra of filamentous bacterial viruses are dominated by scattering from vibrations of the protein capsomers. The amino acid compositions of coat proteins in Pf1 and fd strains are recognized by their different side-chain vibrational frequencies. However, the conformationally sensitive amide frequencies indicate that Pf1 and fd coat proteins have the same α-helical secondary structures. Viral DNA backbones do not exhibit the A-type geometry.