In some newborns with vital distress, conventional umbilical artery catheterization cannot be performed: in our series, this occurred in 34 out of 248 attempts. In 28 of these 34 infants, catheterization succeeded when hypogastric cut-down of an artery was carried out. Two of the 6 failures were due to a minor complication at the time of the cut-down, while two others occurred in infants presenting a single umbilical artery. The usual cuse of failure of conventional catheterization is probably laceration of the artery wall and ensuing subintimal fistulas and perforation.