The authors examined 34 tendons under the electron microscope, excised within 48 h after rupture of the tendons. The tendons did not exhibit any signs of inflammation or lipomatosis, but fine-structurally marked hypoxic alterations in the tenocytes could be seen. The degenerative (hypoxic tendinopathy appears in three phases, and the hypoxic lesions of the tendon occur at multiple foci or diffusely, and the various phases can exist simultaneously.