The effect of an elapsed interval of time between injury and operative repair of the flexor tendons was investigated in a canine model. Transected intrasynovial flexor tendons were repaired either immediately or after a delay of seven or twenty-one days. The biomechanical, biochemical, and morphological characteristics were compared at three and six weeks. The values for angular rotation, linear excursion, ultimate load, and linear slope were determined; concentrations of collagen and reducible collagen cross-links, an index of newly synthesized collagen, were measured; and the ultrastructural morphology of the tendons was examined by high-voltage electron microscopy. For the tendons that were repaired immediately, the values for angular rotation were 9.4 +/- 3.2 and 13.0 +/- 3.7 degrees at three and six weeks; for those that were repaired at seven days, 4.1 +/- 1.3 and 2.5 +/- 1.4 degrees; and for those that were repaired at twenty-one days, 2.7 +/- 0.8 and 4.7 +/- 0.7 degrees. There was a significant effect of the delay until repair on the angular rotation and linear excursion in all three groups (p less than 0.005 for both). Tensile testing of the bone-tendon complex revealed no significant effect of the delay on the values for ultimate load (p greater than 0.05). There were no significant differences in total concentration of collagen at the sites of repair or in the levels of reducible Schiff-base cross-links (indicators of newly synthesized cross-links) in tendons from the three groups.(ABSTRACT TRUNCATED AT 250 WORDS)