The intra-operative establishment of some impairments of the median nerve, in patients who are operated for carpal tunnel syndrome and who previously received several local injections of corticoids, led the authors to try to see the respective responsibility of the compression and of the injection in the degenerative process. In 60- dog cubital nerves, it has been possible, to study different parameters by intra and perineural (recurrent or not injections: the puncture, the dilatation, the solvents, the benzylic alcool and two long action corticoids very often used (triamcinolone acetonide, cortivazol). In the first of our series, the injections were done around the nerve and inside the nerve under visual or blind control (as for an infiltration). The nerves are then cut off after 1, 2, or 3 months. In the second of our series, the injections were done in the same way, but recurrently on the first, second and third month, and the nerve was cut off within the fourth month. An electrophysiological study was performed before taking the samples; they were then prepared for reading on the optical and electron microscope. The results show lesions characterized by an epineural spumous sediment, a localized decrease in the large fibers under the perineurium in the first and second series. These impairments seem to be diminishing with time. However when the injections are done recurrently, the lesions are more important, showing a wallerian degeneration and regeneration.