At the conclusion of the second season episode "The Christmas Show," which aired on December 25, 1967, The Monkees performed "Riu Chiu," a traditional Spanish carol dating from the 16th century.
An official studio version was recorded in October 1967, featuring Monkees producer Chip Douglas on vocals who was substituting for an absent Davy Jones. It went unreleased until 1990's Missing Links Volume Two.
It is likely that The Monkees learned the song from Douglas, who himself performed it with his former band The Modern Folk Quartet on their 1964 album Changes.
In a 2012 interview with the Chicago Sun-Times, Peter Tork revealed his admiration for "Riu Chiu."
"I would say my favorite song we ever did was 'Riu Chiu.' It's an a cappella song, all in Spanish, that we did only once before TV cameras, and the harmony blend was perfect. It's totally crackerjack!"