Purpose: The migratory response of surface fibroblasts to flexor tendon injury was studied by their selective labeling with a vital dye. Method: The surfaces of 30 rat deep flexor tendons were bathed in 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine percholate (Dil), a vital dye for 5 minutes. The residual dye was removed by thorough irrigation. A partial tenotomy was made in the stained section by cutting out a central window. Semiquantitative cell counts and position of stained fibroblasts were noted by examination under fluorescent light at 0, 1, 3, 5, and 7 days. Results: The surface fibroblasts readily took up the vital dye at day 0. By day 1 dyed cells had moved into the cut. By day 3 they had migrated laterally into the core substance of the tendon. Core dyed cell counts at days 1, 3, 5, and 7 were significantly different compared with day 0 core dyed cell counts. Conclusions: This cell migration from the surface of the cut to the tendon core is likely to be vital in the early stages of tendon healing. Copyright © 2003 by the American Society for Surgery of the Hand.