http://news.bbc.co.uk/2/hi/entertainment/4886234.stm
Both books explore the theory that Jesus and Mary Magdalene had a child and the bloodline survives to this day.
Mr Baigent and Mr Leigh argued that Dan Brown copied their book's "central theme".
But the judge, Mr Justice Peter Smith, said The Holy Blood and the Holy Grail did not have a central theme in the way its authors suggested.