This paper shows how well-established control system techniques can be introduced to formulate guidelines for clinical testing and monitoring of HIV/AIDS disease and the estimation of HIV/AIDS parameters. It is assumed that the viral load and healthy CD4+T cell in plasma are measured. The objective is to estimate all parameters in the basic three-dimensional HIV/AIDS model. For this purpose, through an analysis of basic system properties, the minimal number of measurement samples for the CD4+T cell and the viral load counts is first obtained. The paper determines then the HIV progression stages when an estimation of all parameters is impossible. Outside these stages, the paper proposes two on-line estimation algorithms for all HIV parameters based on the well-known techniques of adaptive identifiers and adaptive observers. Conditions for parameter convergence are discussed. Simulation results are demonstrated for the parameter estimation using adaptive observers. (C) 2003 Elsevier Ltd. All rights reserved.