Brown said ''The Holy Blood and the Holy Grail" was ''one of the books in the mix" when he and his wife, Blythe Brown, were researching the novel.
He acknowledged ''reworking" passages from the earlier book.
''That's how you incorporate research into a novel," Brown said.
Both books explore theories -- dismissed by theologians -- that Jesus married Mary Magdalene, the couple had a child, and the bloodline survives. The lawyer for the plaintiffs, Jonathan Rayner James, spent the morning citing passages from ''The Holy Blood and the Holy Grail" that he said had near equivalents in ''The Da Vinci Code."
''I'm sorry, again, I have to disagree," said Brown, who appeared frustrated at the lawyer's painstaking and sometimes repetitive questioning. ''These are points of history that were available in a lot of other books we were using."
If Baigent and Leigh secure an injunction to bar the use of their material, they could hold up the scheduled May 19 film release of ''The Da Vinci Code," starring Tom Hanks and Audrey Tautou.
Patrick Janson-Smith, who was involved with both books as former publisher of Transworld, a division of Random House, took the stand briefly to support his former employer.
In a witness statement, Janson-Smith said he saw similarities between the two books, but no evidence of copying.
'' 'The Holy Blood and the Holy Grail' purports to be nonfiction; 'The Da Vinci Code' is a thriller," he said. ''I thought the latter was a romping piece of good fiction. Like any thriller, no doubt it took ideas from any number of sources."
