- Fourier-Transform Infrared Spectroscopy (FTIR) employs a unique approach to optical diagnosis of tissue pathology based on the characteristic molecular vibrational spectra of the tissue. The architectural changes in the cellular and sub-cellular levels developing in abnormal tissue, including a majority of cancer forms, manifest themselves in different optical signatures, which can be detected in infrared spectroscopy. The biological systems we have studied include normal, premalignant (polyp) and malignant human colonic tissues from three patients. Our method is based on microscopic infrared study (FTIR-microscopy) of thin tissue specimens and a direct comparison with normal histopathological analysis, which serves as a `gold' reference. The normal intestine tissue has a stronger absorption than polyp and cancerous types over a wide region in all three cases. The detailed analysis showed that there is a significant decrease in total phosphate and creatine contents for polyp and cancerous tissue types in comparison to the controls.