The U.S. Department of Agriculture says it is investigating a possible case of mad cow disease.
U.S. officials say a recent test on a cow slaughtered in November returned a positive result after previous tests were negative.
A brain tissue sample has been sent to the British laboratory in Weybridge for analysis. Results are expected in a few days.
U.S. officials say the cow did not enter the food supply, and U.S. beef is safe to eat.
Agriculture Department Secretary Mike Johanns told reporters Friday he is so confident about the safety of U.S. beef that he is going to enjoy a big steak.
The United States discovered its first mad cow case in December, 2003, but no other cases have been confirmed since then.
Some information for this report provided by AFP, AP and Reuters.