Introduction Zinc,an essential trace element in the human body,is known to serve as the active center of approxi-mately 300 enzymes.Zinc deficiency causes various pathological conditions such as growth retardation,immunodeficiency,and neurological degeneration.Zinc deficiency is typically the result of inadequate dietary intake of zinc,the recommended dietary allow-ance for zinc has been presented for healthy individ-uals in the“Dietary Reference Intakes for Japanese,2005”by the Japanese Ministry of Health,Labor,and Welfare. However,we have recently reported that zinc deficiency is common in elderly bedridden patients receiving long- termenteral nutrition based on the recommended dietary allowance,and that zinc deficiency may be associated with increased suscepti-bility to infections in those patients.On the basis of the findings,we have proposed that zinc preparations should be added to the standard enteral formulas to prevent infectious diseases in elderly bedridden patients.Ordinarily,zinc preparations used for zinc therapy are inorganic salts(e.g.,zinc sulphate,zinc picolinate,or zinc chloride)and organic compounds(e.g.,polaprezinc or zinc gluconate).Previous studies have revealed the different activities for zinc therapy between inorganic salts and organic compoundsWe carried out a randomized crossover study to compare organic zinc compounds with inorganic zinc salts,looking at whether there was a difference in their effects on serum zinc and cupper concentrations in elderly bedridden patients receiving long-term stan-dard enteral nutrition.We used zinc chloride as an inorganic salt and polaprezinc as an organic com-pound.Polaprezinc［N-(3- aminopropionyl)-Lhistidinato zinc］,a chelating compound of zinc ion and L- carnosine,is commonly used in the treatment of gastric ulcers in Japan.7 In addition,we carried out a pilot study to examine the therapeutic effects of polapr- ezinc on pressure ulcer healing in elderly bedridden patients receiving long-term standard enteral nutrition because zinc is essential for the wound-healing process.