The effects of experimental nerve fiber compression on the morphology of nerve cell bodies were studied. Rabbit cervical vagus nerves were crushed or subjected to compression at 0 (sham compression), 30, 200, or 400 mm Hg for 2 h. Morphometric measurements and light microscopical evaluation of the nerve cell bodies in the nodose ganglion were carried out 7 days after the injury on the injured and control sides. Crush and compression at 30, 200, or 400 mm Hg induced a slight decrease in total cell profile area compared with the control side, but it was not related to degree of injury. There was a marked decrease in the ratio between nuclear and total cell profile area (nuclear volume density) after compression at 200 and 400 mm Hg, as well as after crush, and to a lesser extent after compression at 30 mm Hg. Compression at 30, 200, or 400 mm Hg as well as crush of the vagus nerve induced migration of the nucleus to the periphery and dispersion of Nissl substance in the cytoplasm of the nerve cell bodies. Sham compression induced no obvious changes in total cell profile area, nuclear volume density, or migration of nucleus. There was a somewhat increased percentage of cells showing dispersion of Nissl substance in sham-compressed animals than in controls. The results show that nerve fiber compression induced pronounced reactive changes in nerve cell bodies, even at low pressures, corresponding to those found in human carpal tunnel syndrome. Such pressures are known to induce reversible inhibition of fast axonal transport as well as inhibition of retrograde axonal transport. The nerve cell body changes in the nodose ganglion may thus be a reaction to disturbances in axonal transport.