OSAKA — Santen Pharmaceutical Co., the nation's leading maker of eyedrops, has begun recalling its products after an extortionist threatened to contaminate its eyedrops with an undisclosed substance unless it pays some 30 million yen in cash.

Takakazu Morita, president of the Osaka-based company, told reporters Thursday that Santen has started recalling all of its 24 types of eyedrops for use by the general public and asked that the public temporarily refrain from buying its products.

Telephones at Santen's headquarters were flooded with calls from concerned retailers and consumers Friday, and one company official said that while no one was counting, the number of calls may have totaled 1,000 or so by midmorning.