Carefully timed doses of X-rays permitted the severed spinal cords of laboratory rats to regenerate in experiments whose findings were reported today. The findings could hasten the long-sought goal of healing humans with devastating spinal injuries.

Regrowth of severed spinal nerves, along with some functional recovery of paralyzed hind legs, occurred in about one-third of the adult rats who received X-ray radiation three weeks after their spinal cords were cut.

Nurit Kalderon, who led the studies when she was at Rockefeller University in New York City, thinks the X-rays kill certain cells that interrupt a natural tendency of spinal nerves to repair themselves following injury.

Kalderon and Dr. Zvi Fuks of the Memorial Sloan-Kettering Cancer Center reported their findings in two studies appearing in the Proceedings of the National Academy of Sciences.

Kalderon believes X-ray treatment could become a therapy for humans with spinal cord injury, but said considerably more research is needed.