This thesis is a report of a study of the effect of cryosurgery on three areas of particular clinical significance, skeletal muscle, peripheral nerve and horse skin. Light histology and electron microscopy were used to study the normal and treated tissues. The report is divided into three sections. Section one is concerned with the effect of cryosurgery on the biceps femoris muscle of the Guinea pig. The second section describes the same treatment applied to the sciatic nerve of the Guinea pig. The horse was used as the experimental animal for the third part of the investigation into the effect of cryosurgery on skin. The degenerative and regenerative changes which occurred in the tissues after cryosurgery were studied. The low temperature (-200°C) applied via a cryosurgical unit produced severe and rapid degenerative changes within all three tissues. By twenty four hours after treatment the damage to the tissues studied was extreme. The onset of regeneration was also rapid and by one week after treatment all three tissues showed active regeneration. In the study of skeletal muscle continuous and discontinuous regeneration of muscle fibres was observed. Two types of discontinuous regeneration were identified. The non-myelinated nerve fibres were less susceptible to cryosurgical injury than the myelinated fibres. The regenerated non-myelinated axons were smaller and more numerous than the myelinated fibres. Stages in the myelination of regenerated nerve axons were observed. Healing of the skin was completed rapidly and without the complications frequently seen after conventional surgery. Collagen fibres and the basal lamina were more resistant to cryosurgical treatment than other tissue components. This factor was thought to play an important role in regeneration of cold injured tissues.