A letter handwritten by Bob Dylan during a four-night stint at Toronto's Massey Hall decades ago is being sold by a U.S. auction house.

The one-page letter, provided to CBC News by RR Auction via email, contains a letterhead from the Park Plaza Hotel. It is signed by the now 74-year-old superstar, who changed the pop music landscape back in the 1960s with songs like Blowin' In The Wind and Mr. Tambourine Man, not to mention groundbreaking albums like Highway 61 Revisited and Blonde On Blonde.

The letter, which was written to a friend named Steve, is not dated, but the auction house said it is believed to have been penned by the musician in April 1980 while he was performing at the historic music hall.

"We are up in Toronto singing and playing for about 3000 people a night in a downtown theatre," Dylan wrote, calling the city "beautiful and clean."

Robert Livingston, executive vice-president at RR Auction, said the musician had become a religious man and held nightly sermons, but was frustrated to find more people interested in lining up to see the movie Apocalypse Now "than to be baptized and filled with the Holy Ghost."

"By the time Dylan arrived in Toronto for his legendary Massey Hall run as part of the Bob Dylan Gospel Tour, he had been preaching hellfire and brimstone for about a year since converting to Christianity," Livingston said.

"Dylan's songs, too, took on a spiritual tone, and although he declined to play his former hits, his songwriting skills remained," the executive added.

"This remarkable letter offers enormous insight into Dylan's thoughts during a critical period of his career, and such lengthy handwritten material by Dylan is of the utmost rarity."

Bidding for the item began Thursday and is set to conclude on May 19, the auction house said. As of Friday at 9:50 p.m., a bid of $4,431 US was placed for the signed letter.