Rhino horn 'more expensive than gold'
9 February 2014 Last updated at 20:33 GMT
The global rhino population is continually at risk from poachers, who hunt the animal for its horn and then sell it to traditional medicine practitioners in Asia.
An investigation for BBC Newsnight into the illegal trade in Vietnam took Sue Lloyd-Roberts to Hanoi.
During undercover filming, she was offered rhino horn for $6,000 for 100 grams - more than the current price of gold in the country.
The seller told her he obtained the horn legally during a licensed hunting trip to South Africa.
However, hunters are required by law to keep the horn intact as a hunting trophy. To cut it up, or to sell it, is illegal.
You can see more on this story on BBC Newsnight on Monday, 10 February at 22:30 on BBC Two.