MIAMI -- Local 10 investigative reporter Julie Summers went undercover inside a South Florida lab where human testing is done on medications before they hit the pharmacy.

The lab does drug testing for major pharmaceutical companies. The medicines are tested on people who, in exchange for money, allow their bodies to ingest with chemicals.

Hundreds of people routinely go to SFBC International in Miami to test new drugs. Testing on humans is necessary. But, because there are risks, it is not a job for just anyone.

One human test subject told Local 10 he was paid $1,000 for a week of testing. He called it "a nice hunk of money" that he "didn't have to sweat for". But some experts have concerns about what happens at SFBC International.

Summers found some of the human drug testers offer their bodies over and over. One patient, for example, told Local 10 that he's been "doing it for two years about every other month."

Human test subjects are told to wait at least four weeks between clinical studies. But biochemist Jay Foster worries that a month may not be long enough for a person's body to flush out residual medicine.

Foster said some people might have residues in their system up to 60 days. And he said he feels that may compromise drug-testing results for the next medicine tested.

Ken Goodman, director of bioethics at the University of Miami, agrees. He told Local 10 it's important to make sure that people "don't become repositories for all sorts of chemicals." He also is concerned that because most volunteer testers are poor, they are not making informed decisions when they sign the lengthy consent forms. Some consent forms are 13 pages long.

Goodman and Foster also said they feel there are ethical concerns about the way the human testers are paid. SFBC International forms clearly state that patients make about 15 percent more money if they stay until the end of testing. That, according to Goodman, raises "real bright ethical flags."

Some believe a solution is stricter controls by the government. Right now, in fact, a U.S. Senate Committee is investigating SFBC Interntional's business practices. SFBC International told Local 10 it is cooperating with the request for records.

Local 10 wanted to talk to SFBC International about the issues raised in its report. SFBC International refused an interview and instead sent Local 10 a letter stating that because of patient privacy, the company could not answer many of the questions. SFBC said all of its studies follow established industry and regulatory guidelines.