Laser welding of tissues is an experimental surgical technique for the binding of tissues. The difficulty in the clinical implementation of this technique arises from the difficulty in defining the optimal conditions under which a satisfactory weld is formed. Temperature measurements of laser irradiated tissues are difficult to perform and experiments have produced conflicting results. Fiber optic radiometry allows temperature measurement of laser irradiated tissues by remote sensing of emitted infra red (IR) radiation. We developed an IR radiometer capable of accurate temperature measurements (± 0.2°C). Utilizing this radiometer for the monitoring and control of CO2 laser irradiated tissues we achieved temperature control of ± 2.5°C of tissues during welding. This system was used to perform laser welds on the urinary bladders of rats. The strength of the welds was recorded for different welding temperatures, and maximal strength was obtained at 55°C and 12 sec.