Structural changes in cod myosin after formaldehyde (FA) addition with and without subsequent freezing at – 18°C were examined by Raman spectroscopy, ANS hydrophobicity, solubility and SDS-PAGE profiles. Protein solubility decreased by >90%, whereas ANS fluorescence showed little change, possibly due to a balance between soluble and insoluble fractions differing in exposed hydrophobicity. SDS-PAGE showed irreversible insolubilization at increasing FA concentration, especially after frozen storage. Raman spectral analysis indicated a change in secondary structure of aquacide concentrated myosin preparations, from 95%α-helix in the control (no FA) to 60% after 12 mM FA treatment. Changes in vibrational modes assigned to aliphatic residues suggested involvement of hydrophobic interactions after FA addition or frozen storage.