The dollar’s decline against the euro shows no sign of ending. Clearly, currency traders have made a long-term judgment about the relative value of the currencies of the Old and New Worlds. That sounds bad enough. But now there are signs that we’re losing some of the most devoted fans of the greenback: drug dealers, Russian oligarchs, and black-market traffickers of all kinds.

James Grant, of Grant’s Interest Rate Observer,whose animadversions about the dollar and other subjects are as droll as they are pricey, highlighted the latest indignities to befall the once-mighty dollar in his Dec. 17 issue. (Alas, it’s not available on the Web.)

People the world over—central banks, companies, and individuals—like to hold the dollar. It’s stable, liquid, easily convertible, and never goes out of style. The dollar is popular in the official global economy—the money that changes hands through computer terminals, checks, and wire transfers. But it has also been extremely popular in the world’s vast cash economy. For American tourists, Chinese smugglers, Ukrainian arms dealers, and African dictators, the dollar has long been the currency of choice. The fearful and shady, those who subsist on tourism, and residents of countries with unstable domestic currencies love the greenback. Citing Federal Reserve estimates, Grant writes that “between 55% and 70% of the $703 billion of U.S. currency outstanding circulates outside the 50 states.”

The United States benefits greatly from the fact that the dollar is the world’s reserve currency. Many of the $100 bills circulating throughout the globe are essentially loans that we never have to pay back. Americans use them to buy goods, services, or other currencies. But many of those bills never return to our shores to be redeemed for anything we make or produce. Instead, they stay under mattresses in Bogotá, circulate in Iraq, and are stashed in bank accounts around the world.

But among a subset of global cash connoisseurs, the dollar is losing ground to the euro—and it has nothing to do with concerns over U.S. multilateralism. First, the euro zone has been expanding with the addition of new countries and the continued integration between Eastern and Western Europe. So there are simply more people who accept and use euros now. Since 2002, the growth rate of euros in circulation has far outpaced that of dollars. Add in the euro’s recent strength against the dollar, and the case for Eastern Europeans and euro-neighbors to use euros becomes more compelling. In the 1990s, the dollar was remarkably popular in Russia, where residents had long been deprived of coveted Western imports. But between January 2002 and August 2004, Grant notes, the percentage of private Russian currency transactions employing the dollar fell from 94.1 percent to 84 percent while the euro’s share rose from nothing to about 15 percent.

Finally, in the past two years, euros have also become easier to carry, store, and hide than dollars. Generally, the largest denomination of U.S. currency readily available is the $100 bill. But in the past two years, the European Central Bank has started to print 200-euro and 500-euro bills. These larger bills thus allow for the concentration of wealth in smaller packages. At today’s rates, a 500-euro note is worth $682.

So if you wanted to, say, hide cash by swallowing it temporarily, euros would the obvious (and more comfortable) way to go. And indeed, as Grant notes, in October a drug mule traveling from Spain to Colombia was found to have an unexpected form of contraband in his stomach: $197,000 in euro notes. The same month, Fidel Castro declared that the dollar, which is tolerated as a means for Cuban-Americans to support their relatives in Cuba, was officially currency non grata and that the euro was most welcome.

For most products, losing international drug cartels and corrupt Third World dictators as customers would seem to be a desirable outcome. But these guys represent part of our long-standing and faithful base. If you think pundits are fretting about the slumping dollar now, just imagine what might happen if we start to lose the arms dealers.