Chugai Pharmaceutical Co., the Japanese unit of Roche Holding AG, and Eiken Chemical Co. led gains in health-related stocks in Tokyo trading Monday on speculation that an outbreak of swine influenza in Mexico may increase sales.

Chugai, the Japanese seller of the antiviral drug Tamiflu, rose 14 percent to ¥1,845 on the Tokyo Stock Exchange, the biggest gain since Jan. 6, 2000. Eiken Chemical, a Japanese maker of diagnostic kits, rose 14 percent to ¥733, the most since Oct. 14. The stocks were the biggest gainers on the 33-member Topix Pharmaceutical Index, which rose 1.5 percent.

Daiwabo Co., an Osaka-based maker of antiviral fabric, rose ¥80, or 38 percent, to ¥289, the biggest gain since April 10, 1990.

More than 100 people have died in Mexico from the outbreak of swine flu, normally spread among pigs. Six people in Canada and 20 people contracted the disease in five U.S. states. Ten New Zealand students who recently visited Mexico are "highly likely" to have swine flu, and three more are suspected, Health Minister Tony Ryall said in Wellington.

Japan, where no cases have been reported, will heighten its screening for any signs of swine flu and examine flights from Mexico, Chief Cabinet Secretary Takeo Kawamura said.

The health ministry is monitoring availability of influenza treatments such as Roche Holding AG's Tamiflu at hospitals in Japan and screening visitors from Mexico at airports for fever, Yoshio Namba, head of the office for pandemic influenza, said Sunday.