A method is described for distinguishing 5-position methylation changes of cytosine bases and cytosine-to-thymine mutations and for the detection of single nucleotide polymorphisms (SNPs) or point mutations in genomic DNA, in which: a) a genomic DNA sample is treated with sulfite or disulfite in such a way that all of the cytosine bases that are not methylated in the 5-position of the base are changed in such a way that a base is formed that is different in its base-pairing behavior, whereas the cytosines methylated at the 5-position remain unchanged, and b) an aliquot of the same genomic DNA sample is quantitatively methylated with Sss1 or another methyltransferase prior to the chemical treatment according to a) and c) both of the DNA samples treated in this way are investigated for the presence of cytosine by means of the same analytical method, and d) the cytosine positions that are determined are matched with a reference DNA sequence.