If you lack a high school diploma and want to earn an equivalent credential, be warned that you can't do it on the Internet or through a correspondence program.

The test can only be taken in person at an official General Educational Development, or GED, testing center.

State GED administrators across the country say they have received an increasing number of complaints from individuals who paid steep fees -- up to $500 -- to take what they thought were the official GED tests. Because they are self-supporting, each legitimate GED testing site sets its own rate. The cost ranges between $50 to $75.

The GED tests writing, reading, social studies, science and mathematics. The service said 419,000 adults passed the tests in 2006. It said the 2000 U.S. Census "indicates that more than 39 million adults in the U.S. aged 16 or older -- about 18 percent of the adult population -- lack a high school diploma."

The GED Testing Service "is deeply concerned with a recent increase in the number of Web sites purporting to offer GED testing online or through the mail," said Sylvia E. Robinson, executive director of the service and assistant vice president of the American Council on Education, or ACE, which oversees the GED program.

"Any services that purport to offer a GED credential through any other means are not affiliated with the GED Testing Service or the American Council on Education, may be of dubious value and may deliver a product that is not accepted by employers, colleges and universities or the military."

Ms. Robinson said the GED Testing Service is increasing its efforts to alert the public and education community to Web sites that infringe on the GED trademark and brand.

Ms. Robinson said GED testing is administered locally by each of the 50 states, the District of Columbia, the Canadian provinces and territories, U.S. territories, the U.S. military and federal correctional institutions.

Individuals in the Pittsburgh area who want to locate their nearest testing center should call 412-208-1122.

Ms. Robinson said hiring personnel, college admissions officers and military enlistment personnel who want to verify the authenticity of an individual's GED credential can do so by contacting the agency that administered the tests. A complete list of those agencies can be found at www.gedtest.org by clicking on "Contact your jurisdiction's GED testing program."