A US animal rights group is calling on a New York court to recognise a chimpanzee as a legal person, in what is believed to be a legal first.
The Nonhuman Rights Project wants a chimp named Tommy to be granted "legal personhood" and thus entitled to the "fundamental right of bodily liberty".
The group is planning to file the same lawsuit on behalf of three other chimps across New York this week.
It wants the four to be released from their captivity.
They should be taken to a sanctuary that is a member of the North American Primate Sanctuary Alliance, the group argues.
The group filed the lawsuit on behalf of Tommy on Monday.
"We are claiming that chimpanzees are autonomous - that is, being able to self-determine, be self-aware, and be able to choose how to live their own lives," its founder Steven Wise told the Associated Press news agency.
Scientists' evidence is included in the lawsuits.
"Once we prove that chimpanzees are autonomous, that should be sufficient for them to gain legal personhood and at least have their fundamental interests protected by human rights," Mr Wise said.
Tommy, the group said, "is being held captive in a shed at a used-trailer lot" in Gloversville, New York.
Patrick Lavery, owner of the site where Tommy lives, said the chimp's cage was spacious "with tons of toys".
He said he rescued Tommy from his previous home, where he had been badly treated, but had been unsuccessful in placing him in a sanctuary because there was no room.
"If [the Nonhuman Rights Group] were to see where this chimp lived for the first 30 years of his life, they would jump up and down for joy about where he is now," Mr Lavery told the New York Times.
The lawsuit invokes the common law writ of habeas corpus, the right to challenge unlawful detention.
The group says it is dedicated to changing the common law status of species considered autonomous, and could eventually file lawsuits on behalf of gorillas, orangutans, whales, dolphins and elephants. (BBC)