PURPOSE: Exogenously administered mesenchymal stem cells and bioactive molecules are known to enhance tendon healing. Biomolecules have been successfully delivered using sutures that elute growth factors over time. We sought to evaluate the histologic and biomechanical effect of delivering both cells and bioactive substrates on a suture delivery vehicle in comparison with sutures coated with bioactive substrates alone. METHODS: Bone marrow-derived stem cells were harvested from Sprague-Dawley rat femurs. Experimental cell and substrate-coated, coated suture (CS) group sutures were precoated with intercellular cell adhesion molecule 1 and poly-L-lysine and seeded with labeled bone marrow-derived stem cells. Control (substrate-only [SO] coated) group sutures were coated with intercellular cell adhesion molecule 1 and poly-L-lysine only. Using a matched-paired design, bilateral Sprague-Dawley rat Achilles tendons (n = 105 rats) were transected and randomized to CS or SO repairs. Tendons were harvested at 4, 7, 10, 14, and 28 days and subjected to histologic and mechanical assessment. RESULTS: Labeled cells were present at repair sites at all time points. The CS suture repairs displayed statistically greater strength compared to SO repairs at 7 days (12.6 ± 5.0 N vs 8.6 ± 3.7 N, respectively) and 10 days (21.2 ± 4.9 N vs 16.4 ± 4.8 N, respectively). There was no significant difference between the strength of CS suture repairs compared with SO repairs at 4 days (8.1 ± 5.1 N vs 6.6 ± 2.3 N, respectively), 14 days (22.8 ± 7.3 N vs 25.1 ± 9.7 N, respectively), and 28 days (40.9 ± 12.4 N vs 34.6 ± 15.0 N, respectively). CONCLUSIONS: Bioactive CS sutures enhanced repair strength at 7 to 10 days. There was no significant effect at later stages. CLINICAL RELEVANCE: The strength nadir of a tendon repair occurs in the first 2 weeks after surgery. Bioactive suture repair might provide a clinical advantage by jump-starting the repair process during this strength nadir. Improved early strength might, in turn allow earlier unprotected mobilization.