In this paper, we remove, for semiglobal output feedback control of uncertain nonlinear systems, a previous requirement that the high-frequency-gain sign be known a priori. Our proposed control scheme is also of the high-gain observer-type, but it involves a switching between two forms of control, The underlying idea is that with the help of the high-gain observer, the high-frequency-gain sign can be identified on-line, provided the designed control satisfies some domination condition.