Recent positive drug tests by two cyclists suggest there is a new, cutting-edge substance making its way to athletes looking for performance- enhancement: FG-4592, an experimental drug that increases production of red blood cells but has not yet been approved for human consumption.

Athletes have long found surreptitious means of obtaining banned performance-enhancing drugs, but with FG-4592, there actually may be a far more straightforward way - simply by ordering it from chemical-supply companies online.

And that, said Don Catlin, an expert on testing for banned substances, is something new to him. Athletes have gotten banned drugs from websites in China, he said, but what they receive is not always what they tried to order. The companies selling FG-4592 are not marketing it to athletes or individuals who want to take it; they emphasize that what they are selling is a chemical that is intended only for researchers. But according to Catlin, a consultant on drug testing and former director of the UCLA lab that performs drug tests for the Olympics, that may not stop a determined athlete.

“What’s amazing to me is that it is out there for sale on the Internet,” Catlin said. This is in contrast with similar performance-enhancers such as erythropoietin, which likewise increases red cell production.

One of the cyclists accused of taking FG-4592, Fabio Taborre of Italy, was provisionally suspended on Monday after testing positive. The other, Carlos Oyarzun of Chile, was expelled from this month’s Pan American Games for the same reason.

Both cyclists’ suspensions were based on a single test; they are awaiting the results of a backup sample. Oyarzun has denied taking FG-4592.

In theory, FG-4592 is available only to participants in clinical trials being conducted by AstraZeneca and FibroGen. The drug is in the final stage of testing but not approved for sale.

But at least three chemical-supply companies sell FG-4592. A person can simply go to a website, click on FG-4592, add it to a cart, pay with a credit card and even get it sent via overnight delivery. The hitch, though, is that the buyer has to be a researcher.

“You have to have something in writing saying you will be using it for research purposes,” said Jane Lee, a technical-support specialist at Selleck, a company that sells the compound and advertises it to be 99.36 percent pure. Lee added that the compound has to be sent to a university or research facility.

The effective dose depends on the size of the person. But Selleck provided a helpful chart listing proper doses according to size and body surface area, for animals as varied as mice and baboons.

Unlike EPO, a blood booster that is injected, FG-4592 is taken as a pill. It spurs the body to make more red blood cells, in part by stimulating the production of EPO, a hormone used in red blood cell production that has been prevalent in professional cycling for years.

Athletes know that anything that gives them more oxygen-carrying red blood cells will make them faster and improve their endurance. Their means have run the gamut from the work-intensive and legal (such as altitude tents and training at high altitudes) to the chemical and illegal (such as blood doping and injections of EPO).

The new drug is in a class of substances, known as hypoxia inducible factor stabilizers, that is prohibited by the World Anti-Doping Agency, which tests for it via urine samples. More than 600 sports organizations - including the International Olympic Committee and the International Cycling Union, or UCI, which represents cyclists - use the agency’s lists to determine which substances to ban.

There is no other drug like FG-4592, said Abigail Bozarth, an AstraZeneca spokeswoman. She added, “We are unable to comment on how an individual might gain access to FG-4592 outside of a clinical trial.”

At Cayman Chemical, another company that sells FG-4592, Gregory W Endres, vice-president for chemistry, warned that “it would be highly inadvisable” for a person to buy and then consume the chemical. The reason, he said, is that it is not produced somewhere that is authorized to make drugs for human beings.

“This is a research chemical, for research purposes,” Endres said. “Things go through the FDA for a reason.” He would not elaborate on what risks someone would take using Cayman’s compound, which is considered to be 98 percent pure.

Christopher Kelly, a spokesman for the Food and Drug Administration, said the agency did not deal with the prospect of humans’ ingesting drugs sold by chemical-supply companies and intended for research in animals. It is not clear, he said, what risks, if any, they might be taking.