The human immunodeficiency virus infection, that causes acquired immune deficiency syndrome, is a dynamic process that can be modeled via differential equations. In this paper we introduce an output feedback method designed for antiretroviral drug therapy to control the immune response. The purpose of the method is to steer the system to an equilibrium condition, the long-term nonprogressor, which corresponds to an infected patient who does not develop the symptoms of acquired immune deficiency syndrome. The suggested control idea guarantees that the immune state is enhanced to a certain level, which is enough for a typical patient to be driven into the long-term nonprogressor status. (C) 2009 Elsevier Ltd. All rights reserved.