There is evidence that direct current (DC) stimulation promotes neurologic recovery in spinal cord injury. The authors conducted a morphometric analysis of axons at the site of spinal cord injury in adult rats treated with a DC field. Ten rats received a 17-g and 15 rats a 53-g clip compression injury and were treated with either a sham (control) or a functioning DC stimulator for 8 weeks. Five normal rats were also assessed. There was a significant relation (p less than 0.0001) between the severity of injury and the number of axons at the injury site. After the 17-g injury, there was no significant difference in the number of axons between control and treated rats. However, after the 53-g injury, there were significantly (p less than 0.05) more axons in treated than control rats. Both degrees of injury caused preferential destruction of large-calibre axons. Subsequent analysis showed that the axon diameter of treated rats with 17-g or 53-g injury was significantly greater (p less than 0.05) than that of control rats with 17-g or 53-g injury. These data, for the first time, show that the application of a DC field increases the number and calibre of axons at the site of a spinal cord injury and enhances the survival or regrowth of axons following spinal cord injury in the rat.