A mechanism and method for steering a surgical instrument inserted into an endoscope such as a ureteroscope, nephroscope, or cystoscope, and/or for steering the endoscope, utilizes a shape memory structure secured to the surgical instrument or to the endoscope, the shape memory structure having a transformation temperature slightly greater than that of the human body so that bending of the shape memory structure, and therefore of the surgical instrument or endoscope, may be carried out by raising a temperature of irrigation fluid in the working channel. The steering mechanism may be used as a supplement to a tensioned-wire steering mechanism, reducing stress on the endoscope shaft and extending the service life and repair interval of the endoscope. In addition, when the surgical instrument is a glass optical fiber, the steering mechanism may be used to ensure that a tip of the optical fiber is within the field-of-view of fiber optics incorporated into the endoscope.