They were whacked into a lake in 1891 as part of an exhibition by sporting legend Old Tom Morris but now they are worth far more than their weight in gold, if only they can be recovered amid thousands of other balls at the bottom of a Donegal lake.
The golfer's own 'gutta percha' balls were worth just a shilling as he practiced his swing on the banks of Lough Salt in Co Donegal.
More than a century later the little pieces of sporting history are worth €20,000 each, or up to €400,000 if all 20 are found.
Divers are now searching for the sunken treasure that has been hidden for 121 years.
At the end of the 19th century, four-times Open champion Old Tom was in the county to design the Rosapenna golf course.
Local historians record an incident where the Scottish golfer stopped off at nearby Lough Salt to practise his swing.
Now diver Gus O'Driscoll and four members of the Delta Specialist Diving Club are hoping they can find the rare old golf balls.
"There are literally thousands of balls at the bottom of Lough Salt because stopping off to hit golf balls there has been a tradition going back to Morris's time," he said.
"We have recovered some golf balls from the early 1900s but we haven't located Morris's golf balls as yet."
Morris's son ' Young Tom ', golf's first progidy, won four consecutive British Opens, a feat which has never been equalled.
Balls deep in Donegal lake
Lough Salt is one of Ireland's deepest lakes. Surveys have reportedly indicated a depth of 83 metres.
The diving team has been training for the exercise for more than a year, diving to depths of 75 metres.
"The balls we are looking for were designed by Morris himself and he used them when he won the Open four times in the 1860s.
"They are made of rubber and can fetch up to €20,000 each at auction, but they may be worth more if they were actually used by Morris himself. It would be fantastic to get one of them."
The diving team have already decided what to do if they do get their hands on what is one of the world's rarest golf balls.
"We'll donate it to the Rosapenna Golf Club," said Mr O'Driscoll.
"There's a statue of Old Tom Morris at the entrance to the course he designed and it would be lovely to give the club one of his balls to put on display in the club house."
Video: Gus O'Driscoll diving in Lough Salt
Old Tom Morris (Wikipedia)
Young Tom Morris (Wikipedia)