Colombians call these black markets “San Adresitos,” and they flourish in every major city throughout the country.

Bogota’s San Andresito is jammed with thousands of tiny stalls packed full of every kind merchandise imaginable, from cheap sunglasses to expensive perfumes and high-tech computers.

Most of what is sold here is brought in by smugglers who don’t pay taxes or import duties, and finance their trade with drug money.

The monetary system of the smugglers is drug money -- the Black Market Peso exchange.

Jesus Giraldo Botero directs international investigations for the Colombian Customs Service. The Black Market Peso Exchange, he says, is how Colombian smugglers get the foreign cash they need to supply their illegal black markets.

Botero: “If you are smuggler in Colombia, you cannot pay through the banks. You know the banks will tell you, ‘Let me see your import documents and the customs clearance process and all the import duties that you pay.’ They have no documents.”

For Colombian Drug dealers, the smugglers need for U.S. dollars provides a simple solution to a complex problem, and the Peso exchange system supplies the grease that keeps an enormous illegal economy humming. Marci Forman, directs the U.S. custom services financial investigation unit.

Forman: “We are talking about millions and millions of dollars. The drug trade is a very lucrative business. And there are actually warehouses stored full of U.S. currency. The currency in the United States is useless to the Colombian drug organizations, which need to get the money back to Columbia.”

Santangelo: “I think money launders have had to be more creative in terms of moving their money out of the country.”

Santangelo: “There has been such a crack down in the United States in terms of the reporting of cash transactions and identification of suspicious activity. I think that’s why people have focused more on this Black Market Peso Exchange.”

According to documents filed by the U.S. Customs Service, in D.C. federal district court, some of America’s best-known, publicly traded companies, like Intel and Merrill Lynch, have unknowingly accepted these payments.

While many U.S. companies have been duped into participating in these schemes, the Customs Service says Bell Helicopter, which it is now pursuing in court, should have known better.

The U.S. Customs Service charges Bell sold a $1.5 million helicopter to Victor Carranza, a Colombian with known ties to drug dealers and right- wing paramilitary groups. And, according to customs officials, he used laundered drug profits to finance the sale.

For this one transaction Bell Helicopter, accepted 25 separate third- party payments from 16 different sources, and the Customs Service says alarms should have gone off at Bell.

Bell Helicopter has denied any wrongdoing, and Bell Officials declined to comment, citing the ongoing court case.

But customs agents and attorneys say there are some simple things all U.S. companies can do to avoid becoming unwitting pawns in a money- laundering scheme. Chief financial officers should be wary of large cash transactions -- and to flag any purchases that are paid for by third parties, and contact the feds if payments seem suspicious.

Some companies cited in the Bell court case have initiated policies to thwart money laundering.

Ironically, as Bell Helicopter continued its court fight over the federal charges, it won a $130 million contract from the U.S. Government to supply 42 rebuilt helicopters for use in the Colombian drug war.

But after months in court, both the feds and Bell say they expect to settle their court case soon.

In Washington, I'm Stephen Henn for Marketplace.