Fifty-five letters written by Vincent van Gogh which have been out of public view for 60 years have been bought by the Van Gogh Museum in the Netherlands.
A new book of Van Gogh's letters is to be published in 2008-9
The letters, including some sketches, were written between 1881 and 1885 to fellow Dutch artist Anthon van Rappard.
"They are of key importance for our understanding of Van Gogh's views and his development as a burgeoning artist," said the Amsterdam museum.
It already holds about 700 Van Gogh letters, mostly to his brother Theo.
The museum stresses the value of the newly-bought letters as "genuine correspondence between artists".
Theo van Gogh introduced Vincent and Van Rappard, who lived in Brussels, in 1880, and the pair corresponded for four years.
They kept each other informed about their work, discussed art and literature, and exchanged sketches, drawings and prints.
The museum says they "felt a certain camaraderie as painters of the common people".
But Van Rappard's criticism of Van Gogh's Potato eaters painting in 1885 soured the friendship and the correspondence ended soon after.
The museum bought the letters from an anonymous private collector via Sotheby's in New York.