In this paper, a generalization of the concept of selective "slaved" pulses in NMR spectroscopy introduced recently by the authors is presented. The shape of these pulses is slaved to that of a signal produced by the sample by the action of an electronic feedback loop. The theoretical analysis is based on results of the theory of nonlinear dynamical systems, which predicts the possibility of performing 90 degrees self-calibrated radiofrequency pulses, through the simultaneous action of a constant radio-frequency field and of a magnetization dependent field of the kind above. Experimental demonstrations show that rotation of the magnetization onto the xy-plane is achieved, regardless of its initial position. Moreover, it is shown to remain stable for more than 50 ms, without significant loss of intensity. (C) 2000 American Institute of Physics. [S0021-9606(00)01213-7].