Catecholamine levels were determined in the submandibular glands of new born rats treated with physiologieal saline solution or large doses of sodium fluoride (10mg/kg) for verying periods of time. In control group, catecholamine levels were gradually increased from fifth day of life until twenty-fifth day of life. When fluoride treatment was started on the fifth day after birth and continued daily to the thirty-fifthday of life, decreased catecholamine levels were obsrved on the fifth, through all experiments, and thirth-fifth day. Daily fluoride treatment from the fifteenth through the thirty-fifth day after birth induced the decreased catecholamine levels which were higher than the levels in submandibular glands of rats treated from the fifth day to the thirty-fifth day after birth with NaF. These experiments suggest that fluoride may be affecting catecholamine biosynthetic mechanisms which were duveloping during the fifteenth to twenty-fifth day of life.