Medium chain acyl-CoA dehydrogenase (MCAD) deficiency is the commonest inherited disorder of fatty acid oxidation. Most clinically ascertained cases are caused by thc point mutation K329E in MCAD gene. The frequency of this mutation as determined by usc of dried blood spots on Guthrie cards and the PCR NeoI digestion method. Using molecular ncwborn screening we found no K329E homozygote and 14 K329E heterozygotes in 2,826 newborns from Moravian area of the Czech Republic. Lower frequency of K329E carriers (1/202)) suggests that the incidence of MCAD deficiency will be probably lower in our population than we expected.