A method of detecting contamination by a microbe of a sample of blood product containing proteins and/or macromolecules and/or cells and/or fragments of cells of blood, or for complementing blood, and in which a said microbe can proliferate, said microbe preferably being a bacterium or a yeast, the method comprising the following steps: a) performing lysis treatment of at least the said microbe(s) that might be contained in said sample of said blood product for analysis after an incubation time t; b) using a mass spectrometer, preferably of the Maldi-Tof type, to take a spectrum of said sample of said blood product or of a protein extract from said sample of said blood product as lysed in this way at a time t; and c) determining whether the sample for analysis is contaminated by comparing the resulting spectrum with at least one spectrum from a Maldi-Tof type mass spectrometer selected from the following spectra: c.1) at least one reference spectrum selected from: c.1.1 - at least one spectrum of a said standard sample or respectively of a said protein extract of said standard sample, said standard sample or respectively said extract of said standard sample being a sample of the same nature as said sample for analysis, but not contaminated; and c.1.2 - spectra of said standard samples or of protein extracts of standard samples of the same nature, each contaminated by a respective known different microbe, said standard samples or said extracts having been subjected to the same lysis treatment; and c.2) at least one spectrum of a said original sample or said extract of said original sample that has been subjected to the same lysis treatment before incubation or after being incubated for a time t' different from t. a) performing lysis treatment of at least the said microbe(s) that might be contained in said sample of said blood product for analysis after an incubation time t; b) using a mass spectrometer, preferably of the Maldi-Tof type, to take a spectrum of said sample of said blood product or of a protein extract from said sample of said blood product as lysed in this way at a time t; and c) determining whether the sample for analysis is contaminated by comparing the resulting spectrum with at least one spectrum from a Maldi-Tof type mass spectrometer selected from the following spectra: c.1) at least one reference spectrum selected from: c.1.1 - at least one spectrum of a said standard sample or respectively of a said protein extract of said standard sample, said standard sample or respectively said extract of said standard sample being a sample of the same nature as said sample for analysis, but not contaminated; and c.1.2 - spectra of said standard samples or of protein extracts of standard samples of the same nature, each contaminated by a respective known different microbe, said standard samples or said extracts having been subjected to the same lysis treatment; and c.2) at least one spectrum of a said original sample or said extract of said original sample that has been subjected to the same lysis treatment before incubation or after being incubated for a time t' different from t. c.1) at least one reference spectrum selected from: c.1.1 - at least one spectrum of a said standard sample or respectively of a said protein extract of said standard sample, said standard sample or respectively said extract of said standard sample being a sample of the same nature as said sample for analysis, but not contaminated; and c.1.2 - spectra of said standard samples or of protein extracts of standard samples of the same nature, each contaminated by a respective known different microbe, said standard samples or said extracts having been subjected to the same lysis treatment; and c.1.1 - at least one spectrum of a said standard sample or respectively of a said protein extract of said standard sample, said standard sample or respectively said extract of said standard sample being a sample of the same nature as said sample for analysis, but not contaminated; and c.1.2 - spectra of said standard samples or of protein extracts of standard samples of the same nature, each contaminated by a respective known different microbe, said standard samples or said extracts having been subjected to the same lysis treatment; and c.2) at least one spectrum of a said original sample or said extract of said original sample that has been subjected to the same lysis treatment before incubation or after being incubated for a time t' different from t.