A man who believes he's the son of former prime minister John Diefenbaker is pleading to have his mother confirm his paternity, now that he's drawn a disappointing blank in his latest bid for genetic certainty.

Exhaustive DNA tests on a tooth found in a museum in Saskatoon were unable to come up with a definitive match to end George Dryden's quest once and for all.

"Unfortunately, so many people have mishandled the material over the years that it has been compromised to the point where it is impossible to obtain a clear DNA profile of Mr. Diefenbaker," the testing company said in a letter this week to Dryden.

"The evaluation we were able to do indicated some matching markers, but the results are inconclusive."

Dryden, 44, who bears a striking resemblance to Canada's 13th prime minister, has been on a two-year quest to nail down his paternity since discovering that Gordon Dryden, the man he always thought was his dad, was not his biological father.

His mother, Mary-Lou Dryden, was a known confidante of Diefenbaker, who was prime minister from 1957 to 1963 and died in 1979. She may have had an affair with the PM that produced Dryden, although Diefenbaker has always been believed to have been childless.

Dryden called the latest DNA dead end "disappointing."

"We're looking for a needle in a haystack trying to get DNA from somebody who's been dead for almost 35 years," Dryden said Tuesday.

"We've pretty much come to the end of the road if we can't get it off his tooth."

The Toronto businessman said the most obvious and viable next step is to find out from his mother who his father really was.

The problem, Dryden said, is that Gordon Dryden is keeping his wife at an unspecified location and won't allow him to see her amid a soured relationship exacerbated by a lawsuit over family money.

Still, if he can't ask himself, Dryden said, perhaps a doctor or some other neutral party or family member could pose the paternity question to his mom.

"Why can't we just get her to say?" Dryden said.

"How could that possibly hurt and that would be the easiest way to end this thing."

Gordon Dryden, a lawyer and former treasurer of the federal Liberal party, has previously refused to talk about the situation. He could not be reached for comment on Tuesday.

Dryden said he still planned to change his name to Diefenbaker in light of an earlier DNA test he said shows he's related to the ex-PM's clan.