The AFL has targeted more than 20 players for specific drug testing as a part of their anti-doping regime.

The blood tests, which are on top of the league's random testing program, are aimed at detecting the performance-enhancing substances EPO and human growth hormone.

Abnormal test results or significant changes in players' body shape or performance are understood to attract the added testing.

"We're ... one of the only sports to test for EPO and human growth hormone and we do, as part of that, at least 20-30 tests for hGH each year," AFL operations manager Adrian Anderson told Channel Nine's The Footy Show.

"I'm as confident as I can be, you can never be 100 per cent sure on these things, which is why you just need to make sure we're doing everything we possibly can to protect the integrity of our sport.

"There are a whole range of reasons, but any sort of big change in performance, change in body shape, (a) best and fairest, success, are all factors in the information used to make sure we're using those tests in a smart way."

The Australian Sports Anti-Doping Agency conduct the random and target tests.

Target testing is becoming more common around the world as sports try to keep pace with increasingly-sophisticated methods of cheating.

In particular, human growth hormone is notoriously hard to detect.

EPO, or Erythropoietin, became the drug of choice for cheating endurance athletes during the 1990s.

It increases the red blood cell count, which in turns improves endurance.

Human growth hormone helps with recovery, enabling an athlete to train more.

St Kilda utility Brendon Goddard revealed drug testing officials had visited his home for early-morning tests twice in three days before the start of this season.

"I wasn't too happy the second time around - I apologised," Goddard said.

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