The secondary structure of cucumber mosaic virus (CMV) was investigated in solution using Fourier transform infrared (FT-IR) spectroscopy. The amide I region of intact CMV revealed a doublet at 1671 cm-1 and 1653 cm-1, respectively. In order to isolate the IR bands arising from the protein backbone of CMV, the FT-IR spectra of the RNA component, isolated by phenol-SDS treatment of purified CMV and subsequent precipitation by ethanol, was obtained separately and digitally subtracted from the intact CMV spectra. After digital subtraction, the amide I region contained two bands at 1682 cm-1 and 1644 cm-1. The former band was ascribed to beta-sheet structures, while the later band occurs in the region between alpha-helix and "unordered" structures. Resolution enhancement of the finger print amide I region was accomplished using Fourier self-deconvolution of the digitally subtracted FT-IR spectrum of CMV which further confirmed the presence of anti-parallel beta-sheet structure in the protein coat of CMV. Chou-Fasman predictions on the the coat protein also revealed the presence of beta-sheet structure in agreement with FT-IR studies.