The stability of folic acid (FA) in mixtures of Total Parenteral Nutrition has been and is a controversial subject, with discussion concerning the influence of factors such as temperature, light and storage time. As regards the stability of the vitamin B12, there are few studies in scientific literature. For all those reasons, we consider it necessary to make a proper study to evaluate the influence of different factors in the stability of both vitamins. The study was made on 3 liter TPN bags of the EVA type, the composition of which was as follows: AA (85g), glucosa (225g), fat (50g), Na (86mEq), K (60 mEq), Ca (15 mEq), Cl (90 mEq), P (17 mmol) acetate (149 mEq) and 10 ml of MVI-12 which contain 400 micrograms of PA and 5 micrograms of Vitamin B 12. Consideration was also given to the stability of these two vitamins in the same diet, to which were added 10 ml of a commercial preparation of oligo-elements. Six TPN bags were prepared (without oligo-elements); two of them were kept in a fridge and protected from the light, two were kept at room temperature and protected from the light and the other two at room temperature without protection from the light. Samples were taken from all the bags immediately after their preparation and after 24, 48, 72 and 96 hours. The same process was carried with other TPN bags which did contain oligo-elements. The method for determining FA and Vitamin B12 was by radioassay.(ABSTRACT TRUNCATED AT 250 WORDS)