Summary1°There exists a new group of vitamins which includes folic acid, vitamin M, the growth factors for L. casei and Str. lactis, the pterins, and perhaps the antipernicious factor.They fulfil biological functions which appear to be as much important as those of the other B vitamins.2°These vitamins are widely spread, they are particularly abundant in leaves, liver, and yeast.3°In Vertebrates, these vitamins are generally synthetized by the intestinal microorganisms.4°The principal lacking symptoms have been studied till now on birds, rats and monkeys. One of their fundamental characteristics is a trouble in the cells formation in the hæmopoietic bonemarrow which appears either as a megalocytary anæmia or as a leucopœnia with granulocytopœnia.5°Various megaloblastic anæmias of man are probably due to a lack in group M vitamins (folic acid). These are probably necessary to granulopoiesis.6°The different vitamins of group M appear to bo chemically similar and are characterized by the presence of a pterin group in their molecule.