WASHINGTON - Oprah Winfrey, whose show has remained the top-rated TV talk show for 20 consecutive seasons, says her success comes from maintaining her principles and serving others.

"My integrity is not for sale, and neither is yours," Winfrey said at graduation ceremonies Saturday for Howard University, recalling times when she was under pressure to change course or avoid topics to boost ratings or appease advertisers. "Do not be a slave to any form of selling out."

Winfrey recalled how early in her career at a TV station in Baltimore, executives told her she was "too black" and "too emotional." She said they tried to have her TV name changed to something more recognizable, but she refused.

Finally, Winfrey was put on a talk show, she said, to run out her contract.

"And that was the beginning," she told 30,000 people who crowded onto the Howard campus.

Winfrey drew repeated big cheers from the moment she took the stage. She called on the graduates to maintain their integrity and to "go forth and serve."

"I stand here as a symbol of what is possible when you believe in the dream of your own life," Winfrey said. "Don't be afraid. All you need to do is know who you are."

Winfrey said that while growing up her grandmother, a servant in 1950s Mississippi, hoped that Winfrey would "get some good white folks" to work for.

"I regret that she didn't live past 1963 and see that I did get some really good white folks - working for me," said.