Biotinidase deficiency is an autosomal recessiv disease in which there is an inability to cleave biotin from biocytin, because of a complete or partial deficiency of biotinidase. Clinically seizures, skin rash, alopezia, developmental regression may occur. In Austria a nationwide screening for biotinidase-deficiency was started in Jan.1986:325672newborns have been screened on their filter-paper blood samples, out of these in 10 patients the dignosis biot.def.has been made by a enzymatic-spectrophotometric method of Knappe. Thus, the incidence in Austria is l:32567;data from a worldwide screening report on an incidence of 1:61067. The mean biotinidase activity has been calculated to be 0,40+0,12nmol/min/mlpl.(normal range:4,01-7,98)this is 6,1+2,4%of the mean normal activity. 6patients were classified as “profound” and 6patients as partial-deficient. In regard to therapeutic regimes we treated only these patients with a biot.def. less than 10%of mean normal activity.(n=6/10mgbiotin/d). The group of children with partial def. is under control up to now. Recently it has been published that also children with a residual activity betw. 10+30%should be treated. Due to recent knowledge clinical symptoms can be avoided and reversed by means of early treatment(5-10mg biotin/d). Therefore a neonatal screening seems to be highly justified and early treatment of all patients is clearly indicated.