In this paper, we consider global adaptive output-feedback control of nonlinear systems in output-feedback form, without a priori knowledge of system nonlinearities. Our proposed adaptive controller is a high-gain linear controller (since we have no knowledge on system nonlinearities), with the high-gain parameter tuned online via a. switching logic. Global stability results of the closed-loop system have been proved. (C) 2005 Elsevier Ltd. All rights reserved.