OBJECTIVE The aim of the study was to develop a suture technique that would be simple and easy to perform, but also strong enough to resist the strength formed during early active exercise protocols. METHODS Thirty flexor digitorum profundus muscle tendons were obtained from lambs aged 12 to 16 months. The tendons were assigned to three in situ repair groups, including the modified Kessler technique, six-strand Savage technique, and a strengthened modified Kessler technique, all combined with an epitendinous suture. Each group was subjected to biomechanical tests and the maximum strength of the tendons to rupture and the power exerted to yield a 3-mm separation were recorded. RESULTS The mean strengths of the tendons repaired with the modified Kessler technique for 3-mm separation and rupture were 29.9+/-2.9 N and 37.0+/-4.0 N, respectively. The corresponding forces were 39.1+/-6.7 N and 51.3+/-6.1 N with the six-strand Savage technique, and 59.9+/-8.3 N and 69.0+/-8.7 N with the strengthened modified Kessler technique, respectively. Forces to produce a 3-mm separation and rupture were significantly higher with the strengthened modified Kessler repair, whereas the lowest forces were seen with the modified Kessler technique (p<0.001). CONCLUSIONS Tendon repair with the strengthened modified Kessler technique provides the highest resistance to both 3-mm separation and rupture. These biomechanical properties may allow safe and active motion without any gap formation in the repair area.