"It's a robot."

"No, it's a brain surgeon."

They're both right. The Unimate Puma 250 is a robot and a brain surgeon. And doctors in Florida expect to use the device on a human for the first time by month's end.

The arm is used to help surgeons find the exact location of brain tumors. Fed coordinates obtained from a CAT scan of the brain, the computer controlling the industrial robot's six-jointed mechanical arm positions a guidance tube directly above the tumor.

The surgeon, through a hole drilled in the skull, can then take a biopsy -- a small sample of the cancerous tissue -- or implant radioactive material in the tumor with less damage to normal brain tissue, shortening hospital stays from five days to one.

"There is no guesswork -- pinpoint accuracy," says Dr. Yik San Kwoh, who developed the computer program for the arm at Memorial Medical Center in Long Beach, Calif. The arm itself was developed by Unimation, a subsidiary of Westinghouse Corp.

In a recent demonstration, it was used to pluck a one-millimeter pellet from inside a watermelon. "At this time, it just helps the doctor," says Kwoh, who adds that the device also could eventually do some of the surgery. "We're leaving this question open. It's a sensitive issue."