Determination of ethanol concentration in a blood sample drawn from a person who caused a serious car crash showed a level which was markedly above the upper limit tolerated legally i.e. 0.08%. At the court hearing the accused car driver challenged the drunken driving charge and claimed that there might have been a mix up of the blood samples, whereby his was replaced by another blood sample, since the tube containing his blood was not marked with his name. The blood sample had been stored without anticoagulants for about 6 months at -20 degrees C. Due to haemolysis it was impossible to determine conventional haemogenetic marker systems. We therefore tried to extract DNA from the blood sample and to determine the restriction fragment length polymorphism (RFLP) by means of five DNA probes recognizing highly polymorphic single-locus systems as described by Jeffreys et al. We analyzed the RFLP's of both the old blood sample and of fresh blood drawn from the accused car driver and we were able to identify the blood sample as certainly having been taken from the accused.