Several publications during the past 10-15 years report on the identification of acarboxyprothrombin (PIVKA II) in a varying proportion of examined newborn and babies (1.9 to 81.5%). These findings prove that the relevant infants were suffering from vitamin K deficiency. Hence, the researchers recommend to continue the prophylactic administration of Vitamin K to newborn. Another argument in favour of vitamin K prophylaxis is supplied by the results of epidemiological studies on the frequency of haemorrhages in newborn and babies caused by vitamin K deficiency. In respect of avoidance of haemorrhages, a single intramuscular injection of vitamin K appears to be the safest mode of application, but repeated peroral administration seems to be practically equally effective. The very frequently performed intramuscular injection of vitamin K is criticised not only because of possible local complications but also because of the greatly enhanced vitamin K concentrations in the blood after the injection. This enhanced concentration is accused of being responsible for the increased risk of malignant tumour growth in those babies who received vitamin K via the i.m. route, compared with the children who had not been given any injection or to whom vitamin K had been administered orally. For this reason vitamin K prophylaxis should be effected in newborn via the oral route (repeated administration), whereas the i.m. route should be an exception. Recommendations to this effect are already on record.