Abstract: The invention concerns a method for the sequence-specific labelling of nucleic acids comprising the generation of labelled nucleic acid fragments by an enzymatic labelling reaction in which a labelled deoxyribonucleoside triphosphate is attached to a nucleic acid primer molecule and the nucleic acid sequence is determined by means of the label, wherein the labelling reaction is carried out in a single reaction vessel with the simultaneous presence of one or several nucleic acid primer molecules and at least two labelled deoxyribonucleoside triphosphates which each contain different labelling groups and different bases and under conditions in which only one single type of labelled deoxyribonucleoside triphosphate can be attached to a nucleic acid primer molecule.