To help prevent accidents resulting from drug use by individuals in safety-sensitive positions, the Department of Transportation (DOT) requires motor carriers to conduct drug testing of their employees. These drug tests involve collecting a urine specimen from employees. To ensure the integrity of the urine specimen and the collection process, DOT regulations provide numerous protocols that outline collection procedures and identify controls to prevent employees from defeating a drug test. Recent media accounts indicate that some sites performing DOT drug test collections may not be adhering to the collection protocols. Moreover, given the different techniques a drug user may employ in an attempt to defeat a drug test, it is possible that a commercial truck driver could defeat a drug test by diluting, substituting, or adulterating a urine specimen in order to obtain a passing result. GAO was asked to perform an undercover operation to determine whether (1) urine collectors followed DOT protocols at selected collection sites and (2) commercially available products could be used to defeat drug tests. To perform this undercover operation, GAO created two fictitious trucking companies and produced bogus driver's licenses. GAO investigators then posed as truck drivers to test 24 collection sites throughout the United States. GAO briefed DOT officials on its results and they agreed with the findings.