Abstract: A method is disclosed for the uniform irradiation of the inner wall of a hollow organ, including the steps of inserting a catheter having a deflated translucent balloon into the interior of the organ; inflating the balloon until it forms a predetermined configuration and distends the inner wall of the organ to be irradiated into a contiguous and congruent configuration; inserting a light transmission fiber having an isotropic light diffuser tip into the catheter so that the tip is positioned at the center of the balloon and, hence, automatically positioned at the center of the wall to be irradiated; and transmitting light through the fiber out the tip whereby light of uniform intensity irradiates the wall.