Maori art adviser Annette Ferguson, of Wellington, plans to sell 60 of Hotere's works painted between 1957 and 1968.
Auctioneer Ben Plumbly, from Auckland, yesterday said Ms Ferguson was given the 58 works on paper - and two on canvas - by Mr Hotere in 1968, the year he returned from Europe and the year before he became a Frances Hodgkins Fellow at the University of Otago.
"This is probably the largest private collection of works of Ralph's that certainly I've ever been aware of and the fact that no-one's ever kind of known it exists until now is pretty fascinating," Mr Plumbly said.
Ms Ferguson stored, rather than displayed, the unframed and unmounted works and Mr Plumbly, in the sale catalogue, said "there is no precedence" for such collections becoming available for sale.
Mr Plumbly said Ms Ferguson did not want to be contacted by the media.
He believed she and Hotere had a close friendship and she "always knew" the collection was very important.
"She's basically guarded it with her life and I think . . . as the works have become more valuable it's become more of a burden for her."
Mr Plumbly said one work was inscribed with the words "A gentle painting for Annette" and many others were also inscribed with her name.
He believed she did not become aware of the monetary value of the collection until about 10 years ago.
