Scientists think MLB's new growth hormone testing is a PR stunt.

A scientist who has worked to develop a urine test for human growth hormone says the blood test baseball plans to use for minor leaguers can only detect the substance for 6 to 12 hours.

Don Catlin said Friday that the test, announced a day earlier by baseball commissioner Bud Selig, is of limited use. In February, a British rugby league player became the first athlete suspended following a positive HGH test.

"The fact that it's been around for a few thousand tests and only one positive suggests that either there's much less growth hormone being used than we thought, which is doubtful, or the period of detectability is really pretty short -- a few hours. It's probably the latter," said Catlin, adding detection probably would work only with "middle-of-the-night testing."

Players with minor league contracts will be given the blood test, which Selig called "a significant step."

Victor Conte, whose Bay Area Laboratory Co-Operative triggered a federal investigation of steroids use and distribution among athletes, also criticized the blood test. He said it would detect little and called it "flawed" because baseball will collect only postgame blood samples.

"It wouldn't take much of an IQ for a player to circumvent this proposed HGH testing procedure," he wrote in an e-mail to The Associated Press. "A baseball player could possibly inject HGH as soon as leaving a ballpark and test negative from a blood sample collected postgame the following day. HGH injections are routinely done at night before bed, so a morning blood sample would be the target. The available test for HGH requires a random blood collection protocol to be considered anything more than a PR move by MLB."