A U.S. grand jury has indicted eight Mexican drug makers on charges they sold steroids to Americans via the Internet in what the Drug Enforcement Administration said Thursday was its largest operation against suppliers of the banned substances.

Indictments in U.S. District Court in San Diego include charges against the eight companies and 11 executives after a 21-month investigation, the DEA said. The businesses sell $56 million worth of steroids to U.S. customers annually, the DEA said.

Alberto Saltiel-Cohen, described by the DEA as a Mexican citizen who owns three of the companies, was arrested in San Diego on Wednesday, the agency said.

Two people suspected of trafficking in steroids were arrested in San Diego and two others were picked up in Laredo, Texas, the DEA said.

Federal agents also have identified more than 2,000 people in the United States who bought steroids from the companies over the Internet. Importing anabolic steroids can be a felony.

"Drug traffickers prey on the belief that steroids enhance ability, but steroids only rob that ability, as we have seen so often from the affected lives of too many youth and professional athletes," DEA Administrator Karen P. Tandy said.

The DEA said 82 percent of the steroids it tests in its laboratories come from Mexico. The indicted companies account for more than half the Mexican supply, it said.

According to the DEA, the steroid manufacturers tried to mask their intent by marketing their products for use in animals. The companies set up Web sites and facilitated ordering via e-mail, the DEA said.

Saltiel-Cohen's companies, Quality Vet, Denkall and Animal Power, are significant U.S. suppliers of Nandrolone, the DEA said. Quality Vet's English-language Web site indicates its products are for veterinary use only.

The other companies and their products are:

-- Laboratorios Tornel, Testosterone Decanoate.

-- Laboratorios Brovel, Nandrolone Decanoate.

-- Pet's Pharma, Testosterone Enanthate.

-- Syd Group, Stanozolol.

-- Loffler, Methandrostenolone.