In 105 rabbits the course of healing was examined at 1, 2, 4, 8 and 12 weeks (21 rabbits per group) after an experimental Achilles tendon rupture. The following treatment modalities were compared: a. operative functional treatment (resorbable suture, Kleinert technique) b. operative functional treatment with fibrin glue c. primary functional treatment. For the functional (after)-treatment a special orthosis was applied. A 7.5 MHz Ultrasound probe was used for the ultrasonographic evaluation. The histological specimens were stained after Masson-Goldner with Azan. Collagen Type III was depicted immunohistologically with polyclonal antibodies. A semiquantitative fibrocytes count was performed. The histological results showed a smooth healing in the prim. functional treatment group reaching parallel orientation of collagen fibers at 12 weeks. In the fibrin glue-group the fibrin was resorbed after 4 weeks without essential influence to the course of healing. In the suture-group a secondary gapping of the tendon stumps was detectable. At 12 weeks the histological evaluation in all groups showed approximately normal tendon pattern. Immunohistochemically all groups showed cell-associated positive reactions for type III-collagen after 1 week with a maximum after 2 weeks. The semiquantitative fibrocyte count in the primary funct. group showed a maximal number after 1 week, in the fibrin glue- and suture-groups the maximal number could be found after 2 weeks. Sonographically an increase in tendon thickness was detectable up to the 4th weeks in all groups. The secondary gapping of the tendon stumps in the suture group could be detected sonographically. The echogenicity of the tendon during the course of healing showed increasing homogeneity and parallelism in all groups. At 12 weeks the echogenicity was comparable in all groups. The experiment could prove the equivalence of the primary functional treatment to operative therapy in Achilles tendon rupture.