A light sensitive substance taken from the herb St John's wort is being used to treat cancer.
Belgian scientists have already used the substance, hypericin, to detect cancer cells.
But they also believe hypericin could be used to actually kill off cancerous tumours.
Professor Peter de Witte, from Leuven University in Belgium, has been perfecting a technique known as Photodynamic Therapy (PDT) for the last nine years.
It works by utilising the light sensitive properties of hypericin to show up the presence of cancer cells.
He said: "We've discovered that especially bladder tumours that can't be detected through endoscopy, can be detected with hypericin."
The technique is currently being used to treat 100 patients in Belgium.
At present, surgery is required to remove cancer cells once they have been located.
But Prof de Witte is working on a new application of PDT to destroy tumours.
Source BBC News