Method for determining, in vitro, the risk for an individual of developing a malignant hemopathy from a biological sample of blood, or of a blood by-product, or of bone marrow from said individual, said method comprising the following steps: a) exposing the biological sample to medium infrared radiation of wavelength ranging from 4000 cm -1 to 400 cm -1 to obtain a spectrum characteristic of said sample; b) Fourier transform processing of the characteristic infrared spectrum of the biological sample in order to obtain a spectral signature consisting of absorbance peaks characteristic of the nature and relative concentrations of the various molecules present in said sample, by virtue of their position, or of wave number, and of their intensity, or of absorbance; c) comparing said spectral signature obtained in the previous step with one or more reference spectral signatures, said one or more reference spectral signatures being obtained from biological samples of the same nature as the analyzed biological sample from a population of reference individuals subjected to the same infrared processing (and Fourier transform) as the analyzed biological sample; and d) concluding that * if the intensities of a first group of peaks in the spectral signature of said individual are significantly different from the intensities of the same peaks obtained in the reference spectral signature(s), then the individual is likely to develop a hemopathy, the first group of peaks corresponding to wave numbers from the following first group: 1330 cm -1, 1445 cm -1, 1478 cm -1, 1493 cm -1, 1505 cm -1, 1507 cm -1, 1520 cm -1, 1526 cm -1, 1544 cm -1, 1571 cm -1, 1602 cm -1, 1668 cm -1, 1674 cm -1, 1676 cm -1, 1697 cm -1, and 2852 cm -1, * otherwise the individual is not likely to develop a hemopathy. a) exposing the biological sample to medium infrared radiation of wavelength ranging from 4000 cm -1 to 400 cm -1 to obtain a spectrum characteristic of said sample; b) Fourier transform processing of the characteristic infrared spectrum of the biological sample in order to obtain a spectral signature consisting of absorbance peaks characteristic of the nature and relative concentrations of the various molecules present in said sample, by virtue of their position, or of wave number, and of their intensity, or of absorbance; c) comparing said spectral signature obtained in the previous step with one or more reference spectral signatures, said one or more reference spectral signatures being obtained from biological samples of the same nature as the analyzed biological sample from a population of reference individuals subjected to the same infrared processing (and Fourier transform) as the analyzed biological sample; and d) concluding that * if the intensities of a first group of peaks in the spectral signature of said individual are significantly different from the intensities of the same peaks obtained in the reference spectral signature(s), then the individual is likely to develop a hemopathy, the first group of peaks corresponding to wave numbers from the following first group: 1330 cm -1, 1445 cm -1, 1478 cm -1, 1493 cm -1, 1505 cm -1, 1507 cm -1, 1520 cm -1, 1526 cm -1, 1544 cm -1, 1571 cm -1, 1602 cm -1, 1668 cm -1, 1674 cm -1, 1676 cm -1, 1697 cm -1, and 2852 cm -1, * otherwise the individual is not likely to develop a hemopathy. * if the intensities of a first group of peaks in the spectral signature of said individual are significantly different from the intensities of the same peaks obtained in the reference spectral signature(s), then the individual is likely to develop a hemopathy, the first group of peaks corresponding to wave numbers from the following first group: 1330 cm -1, 1445 cm -1, 1478 cm -1, 1493 cm -1, 1505 cm -1, 1507 cm -1, 1520 cm -1, 1526 cm -1, 1544 cm -1, 1571 cm -1, 1602 cm -1, 1668 cm -1, 1674 cm -1, 1676 cm -1, 1697 cm -1, and 2852 cm -1, * otherwise the individual is not likely to develop a hemopathy.