The right sciatic nerve of 78 cross-breed rabbits was exposed. Fifty-two of these nerves were treated with 10% DMSO or 10% ethanol for a period of 10 min before being frozen or supercooled. Twenty-six nerves were just supercooled or frozen, these being used for control purposes. A capacity-limited solid silver probe, 15 cm in length and 1 cm in diameter, was employed. Ethanol was used as the cooling agent. The freezing or supercooling temperatures were 0, −5, −10, −20, −25, and −30 °C, and the freezing or supercooling times were 10, 30, and 120 sec. One, two, or four freeze- or supercool-thaw cycles were employed. After electric supramaximal stimulation with 3.8 V, the amplitudes of the action potentials (AP) were measured before and immediately after 1, 3, 5, 10, 20, 30, 60, and 90 min and 2, 5, and 10 days after supercooling or freezing, respectively. The pretreated nerves were examined under light and electron microscopes after 2 days. The damage to the nerve fibers depends on the freezing or supercooling temperature, the freezing or supercooling time, and the number of freeze- or supercooling-thaw cycles. Electrophysiologically, this damage leads to a decrease in the amplitude or complete disappearance of the APs and to a reduction in motor function. The morphological findings were clumping and at times even vacuolization of the myelin sheaths and a thickening of the axon with a loss of microfilaments, microtubules, and mitochondria. First the large, then the medium and small myelinated nerve fibers appeared to be affected. The unmyelinated fibers seem well preserved. No differences in quality but differences in quantity were observed between those nerves treated with cryoprotective agents and the nontreated control nerves. With the latter, the damage was spread diffusely over the whole nerve; whereas with the pretreated nerves, damage was localized in the periphery, primarily where the cryoprobe was applied. DMSO and ethanol have a cryoprotectivc effect on the nerves, and in this respect it would appear, from electron microscopic observations, that fewer nerve fibers were damaged compared with the control nerves and, from an electrophysiological viewpoint, following pretreatment the action potentials had a greater amplitude than that of the control nerves. After pretreatmcnt with 10% DMSO or 10% ethanol, the freezing or supercooling threshold of the sciatic nerves was determined in relation to the freezing or supercooling times and the freeze- or supercool-thaw cycles. With one freeze-thaw cycle this freezing threshold was, for both 10% DMSO and 10% ethanol, −25 °C with a freezing time of 10 sec, −20 °C with a freezing time of up to 30 sec, and −15 °C with a freezing time of up to 120 sec. Consequently, the freezing threshold was higher than with motor nerves frozen under the same conditions without cryoprotective agents (the controls). If these experimental results could be applied in clinical cryosurgery it might be possible to preserve a peripheral motor nerve in the periphery of the cryolesion to a certain extent by injecting such cryoprotective agents around the nerve.