Spoof rock documentary This Is Spinal Tap is to be preserved by the US National Film Registry, its officials have announced.

The 1984 send-up of rock star pretensions joins 24 other films in being selected for preservation by the country's Library of Congress.

Congressional Librarian James H Billington said films were chosen for preservation because half of those produced before 1950, and 80% of those made before 1920, have been lost due to chemical deterioration.

"The selection of a film, I stress, is not an endorsement of its ideology or content, but rather a recognition of the film's importance in American film and cultural history and history in general."

Other movies chosen by the registry include sci-fi classic Alien, children's hit The Black Stallion, John Singleton's 1991 gang movie Boyz N the Hood, and 1938's Melody Ranch, which featured singing cowboy Gene Autry.

The registry now contains 350 films thought to be an important part of America's cultural history.

While Spinal Tap was not the first spoof documentary, its style has been copied ever since.

Alien, released in 1979 and directed by Ridley Scott, established Sigourney Weaver as the first female sci-fi lead actress.

Other film include Vincente Minnelli's 1952 The Bad and The Beautiful, an examination of Hollywood's treatment of its talent, starring Kirk Douglas.

A 1966 surfing documentary, The Endless Summer, also features, as is a 1901 film about the demolition of New York's Star Theater.

The 25 films chosen are:

• Alien (1979)
• All My Babies (1953)
• The Bad and the Beautiful (1952)
• Beauty and the Beast (1991)
• The Black Stallion (1979)
• Boyz N the Hood (1991)
• Theodore Case Sound Test: Gus Visser and his Singing Duck (1925)
• The Endless Summer (1966)
• From Here to Eternity (1953)
• From Stump to Ship (1930)
• Fuji (1974)
• In the Heat of the Night (1967)
• Lady Windermere's Fan (1925)
• Melody Ranch (1940)
• The Pearl (1948)
• Punch Drunks (1934)
• Sabrina (1954)
• Star Theatre (1901)
• Stranger than Paradise (1984)
• This is Cinerama (1952)
• This is Spinal Tap (1984)
• Through Navajo Eyes (1966)
• Why Man Creates (1968)
• Wild and Wooly (1917)
• Wild River (1960)