Studies were undertaken to determine rational dosages of vitamin A and E during long-term total parenteral nutrition (TPN). Four kinds of vitamin prescriptions containing different amounts of vitamin A and E were prepared from commercially available products and/or hospital pharmacy products. Patients were divided into four groups according to the vitamin prescription used. Plasma vitamin levels of different patient groups were determined by a modified fluorimetric method and were compared with those of a normal subject group. The stability of vitamin A and E in TPN solution after admixing was determining by measuring the remaining vitamin contents by high pressure liquid chromatography. From the results, it was concluded that 1) about 50% of vitamin A was decomposed by sunlight (about 2000 lux) 3 hr after admixing and an orange-colored vinyl cover could protect its photodecomposition; 2) vitamin E was stable at any condition tested; 3) 2500 IU of vitamin A and 15 IU of vitamin E could meet the daily requirements; 4) the plasma levels of vitamin A and E were correlative (p less than 0.01); and 5) concomitant administration of vitamin E was essential to keep the poorer level of vitamin A in plasma.