A Quarantine officer will arrange to have your items inspected to ensure they will not harm Australia's environment and plant, animal and human health. Amnesty quarantine bins are available in the arrival area, or on the way to collect your baggage. If you declare prohibited items, you may be given the option of re-exporting them. On this website is a quick Quarantine reference guide which lists commonly-imported items which are prohibited, which must be treated, or which require inspection. It may be illegal to take them out of, or into, Australia.
Severe penalties apply for offences again the Wildlife Protection Act.