The invention relates to a method for analysing the variations in concentration of RNA messengers obtained by transcription of a set of genes comprising the following steps: -- measure the concentration of RNA messengers for each of the genes in the so-called reference cells and in test cells and report the results in a reference list and a test list, calculate a variation value for each gene which is a measure of the difference in concentration of m-RNA for said gene between the reference list and the test list, calculate a normalised variation value for each gene such that the cumulative frequency distribution of a sub-set of normalised variation values corresponding to genes has similar or identical m-RNA concentrations whatever the sub-set under consideration and identification of the genes with m-RNA concentration variations significantly different to normalised variation values.