David Cheng of Taiwan's "Department of Health" said the two shipments, which weighed 24.3 tons, were found to contain beta agonist.

An initial determination was made last week, Cheng said, and the results were confirmed Monday.

"Taiwan's Council of Agriculture has banned beta agonist since last year, and we only started to check beta agonist in pork then," he said.

Spokesman Thomas Hodges of the American Institute in Taiwan said there were no health risks associated with beta agonist, which appears in pork under the trade name Paylean.

"Paylean has been in use since 1998, and there are no health issues associated with it," he said.

Hodges said Paylean maker Elanco, a division of Indianapolis-based Eli Lilly & Co., had applied to the Taiwanese government for approval to use the material in 2001.

Cheng said Paylean remained banned in Taiwan.

Taiwan has a recent history of difficulties with meat imports from North America.

Last month, the island lifted a ban on Canadian beef that stemmed from a mad cow disease scare. Taiwan lifted a ban on US beef imports in January 2006, also related to the disease.