Nearly half of Merck's sales are outside the United States, and foreign currency revenue from these sales translates into fewer dollars as the dollar gains in value.

The longer-term outlook of further dollar gains helped explain the currency's partial rebound in trading in the United States yesterday.

Even some developed markets posted dollar gains that exceeded the American markets' 26.8 percent gain, as measured by Morgan Stanley Capital International's country stock indexes.

Dan Holland, an assistant vice president for the Discount Corporation, attributed yesterday's dollar gains largely to technical factors.

(If the dollar rises, that fund will lose twice as much as the dollar gains, while the ProFunds version is designed to mirror the dollar's movements.)

By contrast, a portfolio of foreign stocks that is not hedged will benefit when the dollar weakens and will be hurt when the dollar gains.

The statement sent its stock up sharply, rising $4.875, to $41.625, in the biggest dollar gain yesterday on the New York Stock Exchange.

Worries over eurozone sovereign debt prompted the dollar gains, as did the removal of the Swiss franc as an alternative safe haven currency in September.

Human psychology reckons that a 1 per cent chance of a $1 million dollar gain is as real as a 100 per cent chance off $1,000 gain.

The 19.9 percent return in the local currencies of the countries in the index translated into a dollar gain of 37.5 percent.