Auctioneers believe a collection of 3,500 Matchbox toys could raise up to £1m when it goes under the hammer on Teesside later this year.
Owner Dr Scott Gillogly of Atlanta, Georgia, is selling the toy vehicles in a series of auctions at Vectis in Thornaby in September.
The models, made by Matchbox between 1948 and 1982, feature cars, trucks, motorbikes and diggers.
Some individual pieces are expected to fetch up to £12,000 at the sale.
Auctioneer Andrew Reed said: "Dr Gillogly mainly built up the collection when he had a lot more disposable income.
"He always tried to buy the best of everything and the condition of the collection speaks for itself."