The use of farm animals as bioreactors to address the growing demand for large quantities and increasing numbers of biopharmaceuticals is of prime strategic relevance to medical advancement.However, it is well known that uncontrolled constitutive expression of foreign genes may cause serious physiological disturbances in the transgenic animals.The main objective of this study is to test the feasibility of controllable gene expression of an exogenous gene in the chicken.We constructed and tested a retrovirus vector designed to express GFP or hEPO gene under the controls of the tetracycline-inducible promoter.Production of GO founder chickens was done by infecting blastodermal cells of freshly laid eggs with concentrated retrovirus vector solution.Feeding with doxycycline, a tetracycline derivative resulted in emission of green color ort expression of hEPO from the body without any significant physiological dysfunctions.Successful germline transmission of the exogenous gene was also confirmed.Most notably the expression of the transgenes reverted to the preinduction state by removing doxycycline from the diet.These results suggest that application of tetracycline-controllable expression system in transgenic animals might be a promising solution for the physiological disturbance problems due to uncontrolled constitutive expression of the transgene.