The RSPCA is encouraging people to gamble as part of a new fundraising venture.
The animal charity has written to 400,000 active and lapsed donors, as well as individuals who have had contact with the charity, asking them to take part in a weekly lottery.
Players pay £1 to take part and can win weekly prizes of up to £3,000.
There is also an occasional £10,000 special jackpot.
It is the first time the RSPCA has organised a lottery, although it has run a raffle for supporters for the past 20 years.
The charity will monitor the game's success over the next 12 months before deciding whether to extend it.
Brendon Elliott, donor development manager at the RSPCA, said the lottery provided people with a new way to support its work.
"Many people don't realise that despite being the country's largest animal-welfare organisation we do not receive any government funding and are reliant on voluntary donations," he said.
Direct marketing agency Whitewater, which is responsible for all of the RSPCA's direct response fundraising, developed the campaign.
Senior account manager Lucy Porter said the RSPCA game was the first animal welfare lottery and that the initial response suggested there was plenty of interest in charity lottery games, despite the competition from other charities and the Big Lottery Fund.
She said the game was being mar- keted as fun rather than as an emotive appeal to help the RSPCA. As well as the direct marketing campaign, the lottery will be promoted in leaflets available at the charity's animal centres and online.