A trial is needed to decide if Led Zeppelin's Stairway To Heaven copies its opening notes from a song performed by the rock band Spirit, a judge has ruled.
US District Judge R Gary Klausner ruled that lawyers for the trustee of late Spirit guitarist Randy Wolfe had shown enough evidence to support a case that Stairway To Heaven copies music from his song Taurus.
Taurus was written by Wolfe - who used the stage name Randy California - in either 1966 or 1967, years before Led Zeppelin released Stairway To Heaven in 1971.
The judge wrote that while the songs have some differences, lawyers for Wolfe's trustee may be able to prove they are substantially similar.
Led Zeppelin and Spirit performed at some concerts and festivals around the same time, but not on the same stage.
Judge Klausner wrote that the evidence presented so far represented a circumstantial case that Led Zeppelin may have heard Taurus performed before Stairway To Heaven was created.
Experts hired by Led Zeppelin contend both Stairway To Heaven and Taurus include notes that have been used in music for centuries.
Francis Alexander Malofiy, lawyer for Wolfe's trustee Michael Skidmore, praised the ruling.
He said while many copyright cases are an uphill battle, the judge's ruling brings his client one step closer to getting Wolfe credit for helping create one of the most recognisable song introductions in rock history.
Mr Skidmore was able to overcome statute-of-limitations hurdles to sue over Stairway To Heaven because the song was remastered and re-released in 2014.
A jury trial is scheduled for May 10 in Los Angeles.
The judge's ruling removed Zeppelin band member John Paul Jones from the case. Bandmates Robert Plant and Jimmy Page remain as defendants.
To listen to Taurus, by Spirit, click here.
A trial would represent the third time in little over a year that a Los Angeles jury has heard a copyright-infringement case involving a hit song.
In March last year, a jury found 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 dollars (£5.2 million). A judge reduced the award, and the verdict is under appeal.
Later in 2015, another jury was sworn in to decide or not the Jay-Z hit Big Pimpin' copied the work of an Egyptian composer, but a judge ruled in the rapper's favour before deliberations began.