NSW rugby league player Mitchell Mansfield has been banned from the sport for two years after he was caught importing steroids concealed as herpes ointment.

Two airmail boxes from Thailand, addressed to the Wentworthville Magpies Jim Beam Cup player, were intercepted by the Australian Customs and Border Protection Service on July 8.

The Australian Sports Anti-Doping Authority (ASADA) said the boxes were examined and found to contain several vials labelled "Quality First Genital Herpes Ointment".

The liquid in each vial was analysed and found to contain nandrolone and testosterone, both prohibited substances under the World Anti-Doping Code.

Customs officers seized the boxes and notified ASADA of the attempted importation of performance-enhancing drugs.

ASADA Chairman Richard Ings said the case against Mansfield was then strengthened after financial transactions linked to the importation were uncovered during investigations.

Based on the evidence collected during the investigation, the NSWRL handed down a two-year ban which means Mansfield cannot play until July, 2011.

"Our partnership with customs and border protection is vital in allowing ASADA to detect forms of doping that would not be detected through traditional testing alone," ASADA chairman Richard Ings said in a statement.

"Our intelligence and investigations work is a critical component of a comprehensive anti-doping capability.

"In the last twelve months, 38 per cent of athletes placed on ASADAs Register of Findings for a violation of the doping rules were a direct result of intelligence and investigations work."

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