Structural changes of tussah (Antheraea pernyi) silk fibroin films treated with different water-methanol solutions at 20 degrees C were studied as a function of methanol concentration and immersion time. X-ray diffraction measurements showed that the alpha-helix structure, typical of untreated tussah films, did not change for short immersion times (2 min), regardless of methanol concentration. However, crystallization to beta-sheet structure was observed following immersion of tussah films for 30 min in methanol solutions ranging from 20 to 60% (v/v). IR spectra of tussah films untreated and methanol treated for 2 min exhibited strong absorption bands at 1265, 892, and 622 cm-l, typical of the alpha-helix conformation. The intensity of the bands assigned to the beta-sheet conformation (1245, 965, and 698 cm(-1)) increased for the sample treated with 40% methanol for 30 min. Raman spectra of tussah films with alpha-helix molecular conformation exhibited strong bands at 1657 (amide I), 1263 (amide III), 1106, 908, 530, and 376 cm(-1). Following alpha --> beta conformational transition, amide I and III bands shifted to 1668, and to 1241, 1230 cm(-1), respectively. The band at 1106 cm(-1) disappeared and new bands appeared at 1095 and 1073 cm(-)1 whereas the intensity of the bands at 530 and 376 cm(-1) decreased significantly.