Modern problems in the diagnosis of oncological pathologies using spectroscopic methods of analysis are considered. Fourier-transform IR spectroscopy methods are illustrated by investigation of tissues of breast, thyroid gland, stomach, kidney, lung, and skin excised during surgical intervention. IR spectra of surgical material are compared with data of histological analysis. Spectra of proteins and lipids in malignant neoplasms differ from those in benign tumors and in tissues beyond the pathological focus. Differences in protein spectra are attributed to changes in the supramolecular structure due to cleavage of intramolecular C=OH-N hydrogen bonds. Differences in IR spectra of lipids in neoplasms, when compared with those in normal tissues, are caused by changes in the structure of side chains of fatty-acid radicals appearing in malignant tumors. Spectral signatures of malignant pathology are revealed.Introduction. Timely detection of oncological pathology is of prime importance for selecting effective methods for treating oncological diseases. However, the diagnosis of malignant neoplasms is a very complicated aspect of oncology because tumors often manifest clinically as various symptoms, especially in early stages.The essence of the problem is that diagnostic methods currently used in medical practice such as visual, palpation, ultrasound, and x-ray, in addition to MRI and CT are capable in principle of detecting only a tumorous mass. The final conclusion about whether the detected pathology is benign or malignant is made based on morphological investigations. A correct diagnosis is possible only with careful adherence to procedures for obtaining and processing the material to be analyzed. Important considerations for a reliable diagnosis are subjective factors such as the special professional training and experience of the surgeon and a highly qualified pathologist.The morphological diagnosis of a tumor is established based on a whole set of signatures such as cytological characteristics, cell topography, their relationships to basal membranes, vessels, and the condition of the stroma, which acts as a mediator between neoplasms and the organism as a whole. Morphological signatures of malignancy are idiosyncratic to each organ and tissue and can vary considerably. Therefore, both clinical data and results of laboratory tests are very significant for a differential diagnosis of malignant tumors and elucidation of the factors stimulating malignant growth. Information about the tumor location, its growth rate, and the age of the patient can in several instances play a decisive role in the morphological diagnosis [1]. Nevertheless, available morphological data can in many cases be insufficient for an accurate verification of the pathological (tumor) process so that a conclusion about whether the tumor is benign or malignant is presumptuous in nature [2]. Because fundamental life processes, from single-celled organisms to man, are carried out on the molecular level, novel methods that investigate the pathology o...