Out of caution, the Food and Drug Administration said, people should throw away toothpaste with labeling that says it was made in China. The FDA is concerned that these products may contain diethylene glycol.

The agency is not aware of any poisoning from toothpaste in the United States, but it did find the antifreeze ingredient in a shipment at the U.S. border and at two retail stores: a Dollar Plus store in Miami and a Todo A Peso store in Puerto Rico.

Officials said they are primarily concerned about toothpaste sold at bargain retail outlets. The ingredient in question, called DEG, is used as a lower-cost sweetener and thickening agent. The highest concentration of the chemical found in toothpaste so far was between 3 percent and 4 percent of the product's overall weight.

"It does not belong in toothpaste even in small concentrations," said the FDA's Deborah M. Autor.

The FDA increased its scrutiny of toothpaste made in China because of reports of contamination in several countries, including Panama.

The agency is particularly concerned about chronic exposure to DEG in children and in people with kidney or liver disease.

Agency officials said they had no estimate of how many tubes of tainted toothpaste might have made it into the U.S.

"Our concern today is potentially about all toothpaste that comes in from China," Autor said. "Our estimate is that China makes up about $3.3 million of the $2 billion U.S. toothpaste market."

The agency also issued an import alert Friday for all dental products containing DEG. The alert means toothpaste from China will be stopped at the border, she said.

Companies that make brands previously found with DEG will have to prove the toothpaste is free of the chemical before it's allowed into the country. Meanwhile, all other brands of Chinese-made toothpaste will be stopped for testing, something the agency has been doing since May 23.

The import alert posted by the government says DEG has been improperly used in a variety of sedatives, syrups and cough medicines worldwide. Most recently, a cough syrup containing DEG resulted in more than 40 deaths in Panama last September.

The alert says the agency found DEG in three products manufactured by Goldcredit International Trading in China. The products are Cooldent Fluoride, Cooldent Spearmint and Cooldent ICE. Analysis of the products revealed they contained between 3 percent and 4 percent DEG.

The agency also found the chemical in one product manufactured by Suzhou City Jinmao Daily Chemical Co. in China. Analysis of that product, Shir Fresh Mint Fluoride Paste, found it contained about 1 percent DEG.

China's food safety problems have in recent months become a matter of international concern, a situation reflected in trade talks between Chinese and U.S. officials in Washington last week.