Before Sept. 11, 2001, when federal law-enforcement officials asked FedEx Corp. for help, the company had its limits. It wouldn't provide access to its databases. It often refused to lend uniforms or delivery trucks to agents for undercover operations, citing fears of retribution against employees as well as concerns about customer privacy.

Then came the attacks on New York and Washington and pleas from the government for private-sector help in fighting terrorism. Suddenly, the king of overnight delivery became one of homeland security's best friends.

FedEx has opened the international portion of its databases, including credit-card details, to government officials. It has created a police force recognized by the state of Tennessee that works alongside the Federal Bureau of Investigation. The company has rolled out radiation detectors at overseas facilities to detect dirty bombs and donated an airplane to federal researchers looking for a defense against shoulder-fired missiles.

Moreover, the company is encouraging its 250,000 employees to be spotters of would-be terrorists. It is setting up a system designed to send reports of suspicious activities directly to the Department of Homeland Security via a special computer link.

FedEx's newfound enthusiasm for a frontline role in the war on terror shows how the relationship between business and government has changed in the past few years. In some cases, these changes are blurring the division between private commerce and public law enforcement.