Led Zeppelin's Jimmy Page and Robert Plant have arrived at court to face claims they copied a guitar riff on Stairway To Heaven.
The British musicians are accused of plagiarising the instrumental track Taurus by the US band Spirit when they wrote the classic rock song, which was released in 1971.
A lawsuit has been filed by Michael Skidmore, the trustee of Spirit's guitarist Randy Wolfe - known by the nickname Randy California - who died in 1997 having never taken legal action over the song.
A jury will rule on the case at the US District Court in Los Angeles, where Plant, Page and their bandmate John Paul Jones are expected to give evidence.
Led Zeppelin were the opening act for Spirit when the British band made their US debut in December 1968 in Denver, according to documents filed with the court.
Led Zeppelin's lawyers have argued that both Stairway To Heaven and Taurus use notes and combinations that have been circulating in music for centuries.
The lawsuit comes after a US federal jury found last year that Robin Thicke and Pharrell Williams had copied a Marvin Gaye song to create their 2013 hit Blurred Lines and awarded Gaye's children 7.4 million US dollars (£5.2 million).
A judge trimmed the award in that case and the verdict is under appeal.