Dorsal root entry zone lesions are effective in the control of intractable pain in several types of spinal cord injuries. Traditionally, these lesions have been made with the radiofrequency technique. This is effective, but has the drawback of being laborious, and there is a significant incidence of permanent weakness. We have evaluated the carbon dioxide laser, hoping that it would be both faster and more controlled, thereby offering the chance to lower the complication rate. In comparing a parallel series of radiofrequency and laser dorsal root entry zone lesions along the cat's spinal cord, we observed that the radiofrequency lesion was larger. In addition, it had 3 times more variability in its size than the laser lesion. We attribute this in part to the nature of the laser in making a very precise and reproducible lesion. Second, the extremely brief pulse of the laser, a fraction of a second, means that movement of the spinal cord from respiration and heartbeat and movement of the surgical instrument from the surgeon's hand become far less important in inducing lesion variability. We also studied for 2 months a series of chronic cats; there were no complications due to the laser. This work suggests that the laser is a useful instrument for dorsal root entry zone lesions, but requires more precise aiming and focusing.