At least 35,000 people have taken part in the latest mass protest in South Korea against the government's decision to allow US beef imports to resume.
Waving banners, flags and candles, the crowd gathered in front of City Hall in the capital, Seoul.
South Korea used to be a big market for US beef, but suspended imports in 2003 after a "mad cow disease" outbreak.
The decision to lift the ban has led to weeks of protests based on health fears and discontent with the government.
As a result, the South Korean government has sought extra safety assurances from the US authorities on American beef.
Both governments insist the beef is safe.
Among those taking part in Saturday's protest were Catholic priests, Buddhist monks and labour groups.
Some 20,000 riot police were deployed but there were no immediate reports of clashes.
Protesters chanted slogans urging the resignation of South Korean President Lee Myung-bak, who took office in February and has seen his popularity plummet amid widespread protests.
Under pressure, the government renegotiated the agreement in June, with the US agreeing not to export beef from cattle older than 30 months - which is thought to carry a higher risk of mad cow disease, or BSE.
Nonetheless, public anger in South Korea remains high at what is perceived by many as the government's readiness to cave into Washington and ignore health concerns.
UN Secretary-General Ban Ki-moon, who is from South Korea, has called for a resolution of the political turmoil.