Injuries involving division of the flexor tendons of the hand are a common surgical problem. Sutured repairs must be strong enough to withstand early active movement. Experiments were designed to assess the strength of bonds formed between tendon sections as a result of heating (1) under controlled conditions in a water bath and (2) using a carbon dioxide laser (laser tissue welding). The load (N) and stress (N/cm2) required to disrupt thermal bonds between bovine tendon sections heated for 4 minutes in water peaked at 62 degrees Celsius (13N, 11.3N/cm2). Further experiments revealed the optimal time period for heating to be 9 minutes (21.5N, 20.6N/cm2). A threshold effect was apparent at these parameters. The in vitro strength of sutured, laser welded and sutured and laser welded tendon repairs was compared in a rabbit model. Laser welding alone did not produce repairs as strong as sutured repairs. It did, however, augment the strength of sutured repair. This effect was maximal at a power of 0.1 W.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.