Recent studies have demonstrated an intrinsic neovascular response in intrasynovial healing tendons, introducing the possibility of mitogenic and/or angiogenic capability of intrasynovial tendon. To explore this hypothesis, healing canine flexor tendons were treated with early passive mobilization and the repair sites analysed at three, ten and 17 days. Specimens were mechanically digested and subjected to a standard BALB/c 3T3 mitogenic assay, which measures the capacity of tissue extracts to induce DNA synthesis and cell division in fibroblasts. Results revealed that both control and repaired flexor tendons possessed mitogenic activity, with the greatest activity observed in control specimens. Decreasing activity was noted as the time between repair and analysis increased. These data provide increasing evidence for the flexor tendon's active role in the healing process, and support the concept that mitogenic or growth-promoting factors are associated with flexor tendons and may be released following injury, during the early stages of healing.