Abstract: A pulsation nozzle is adapted for insertion in a drill bit such as a single body or tri-cone bit, for delivery of a pulsed jet of thixotropic drilling fluid during drilling operations. The nozzle defines an inlet orifice (31) communicating with an internal cavity (32) and an outlet orifice (33), the dimensions of which are chosen in such a way as to induce the cyclical propagation of disturbances in a shear boundary defined between fluid passing directly through the nozzle and fluid which is momentarily trapped in the cavity, thereby inducing a self-excited oscillating flow of said fluid within the nozzle, and a rapid pulsing flow emitting from the nozzle.