Last updated: 29 may, 2009 - 12:49 GMT
New fears over anti-malaria drugs
Scientists working with the World Health Organisation say they have found the first evidence of resistance to the world's most effective anti-malaria drugs.
The scientists say that until now the drugs, which are from the artemesinin family, cleared all malaria parasites from the blood within two or three days.
But in recent trials, clearance sometimes took four or five days: an early sign of emerging resistance.
The BBC's Jill McGivering is in Pailin in western Cambodia, where the results of the first international trials are just coming through.
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So how worried should we be?
The BBC's Claire Bolderson asked Dr Pascal Ringwald, the Medical Officer in charge of anti-malarial programmes at the WHO, what is meant by drug resistance.
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First broadcast 29 May 2009
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