In what’s being called a major advancement in organ generation, scientists in the U.S. have “grown” a kidney in a laboratory that was transplanted into an animal and has produced urine.

The researchers are Massachusetts General Hospital say the generation of a functioning rat kidney have resulted in the first steps toward creating useful human kidneys.

The researchers took a rat kidney and washed away old cells using a detergent. Using the remaining web of proteins, blood vessels and drainage pipes they used new cells from the rat’s body to rebuild the kidney. The kidney produced 23% the normal output of urine in the lab but only 5% inside an actual animal.

The lead researcher in the study says that a fraction of normal function is enough when it comes to generated kidneys.

“If you’re on hemodialysis then kidney function of 10% to 15% would already make you independent of hemodialysis,” Dr. Harald Ott told the BBC. “It’s not that we have to go all the way.”

He noted that in the U.S. there are 100,000 patients waiting for a kidney and that only 18,000 transplants happen a year in the country.