Four ticketholders who each won £1 million in the New Year's Day EuroMillions Millionaire Raffle have not yet come forward to claim their windfall, the National Lottery said.
A ticket with the selection of HZH113111 was purchased in the Aylesbury Vale District of Buckinghamshire, another with the selection HZH020202 was bought in the London Borough of Haringey and a ticket was sold in the Borough of Dacorum in Hertfordshire with the selection HYW756634.
The final missing millionaire purchased their ticket in the Blaenau Gwent & Torfaen area of South Wales and features the selection HYW536466.
So far just 21 of the 25 ticketholders who won £1 million in the special New Year's draw have come forward.
The remaining ticketholders have until 11pm on June 30 to make their claim.
A National Lottery spokesman said: "Players across these areas should now be checking their tickets -they could be worth £1 million!
"Try and remember back to New Year's Day and where you may have placed that lucky ticket for safe-keeping.
"This year could be very different with a giant cheque in your hand so turn out your drawers and check trouser pockets - the ticket could be hiding anywhere.
"Another two millionaires are guaranteed to be made every week so don't worry if it isn't your ticket as there are plenty more chances to win in every EuroMillions draw each Tuesday and Friday."
Anyone who believes they have the winning ticket for any of the National Lottery draws within the 180-day deadline should call the National Lottery Line on 0845 910 0000.