Red cell B vitamins, folate and white cell vitamin C were measured in a group of critically ill surgical patients before and following a course of intravenous nutrition. Patients received a widely used vitamin supplementation regimen in the form of one ampoule of water-soluble vitamins daily and recommended doses of intramuscular folate, vitamin B12 and vitamin K weekly. This regimen was adequate to maintain tissue levels of the water-soluble vitamins and folate. Patients with initially low values had normal values at the end of the treatment period.