It is well established that the rumen microbial flora are a rich source of vitamins to the ruminant, and that the faecal bacterial flora are a major vitamin source for coprophagic rodents. There is also good evidence that the gut bacterial flora are a significant source of a range of vitamins to the human. In this paper evidence is presented that gut bacteria are a significant source of a range of vitamins, particularly those of the B group and vitamin K.