The ability to sense and control continuously surface temperatures of a tissue being exposed to laser radiation could standardize parameters and eliminate subjective interpretation of results during laser tissue repair. We describe the development and testing of a control system that enables the operator to maintain relatively specific tissue temperatures for the purpose of laser welding. After initial development, the infrared thermal control system combined with an argon laser was used to repair urethral defects in 45 adult male rats. Repairs were completed using various predetermined temperatures of 50, 60, 70, 80 or 90C. The integrity of each weld was quantitatively determined by measuring intraluminal bursting pressure immediately after repair. In all temperature groups bursting pressures were in excess of 85 mm. Hg. Those performed at 80C produced the strongest weld (analysis of variance p = 0.0001). However, welding temperatures above 70C sacrificed the integrity of the underlying urothelium producing obvious damage when viewed microscopically. We were able to demonstrate that temperature is an objective parameter of tissue welding that can be continuously assessed and controlled during the laser repair of tissue defects to produce effective, predictable welds.