A US appeals court will consider whether chimpanzees are entitled to "legal personhood" in what experts say is the first case of its kind.
Lawyer Steven Wise, who is behind the case involving a chimp named Tommy, has spent three decades seeking to extend rights historically reserved for humans to other intelligent animals.
A mid-level state appeals court in Albany, New York will hear the case of 26-year-old Tommy, who is owned by a man and lives alone in what Mr Wise describes as a "dark, dank shed" in upstate New York.
The lawyer is seeking a ruling that Tommy has been unlawfully imprisoned and should be released to a chimp sanctuary in Florida.
A victory in the case could lead to a further expansion of rights for chimps and other higher-order animals, including elephants, dolphins, orcas and other non-human primates, Mr Wise said.
"The next argument could be that Tommy also has the right to bodily integrity, so he couldn't be used in biomedical research," the Boston attorney said.
Tommy's owner, Patrick Lavery, has made the rare move of waiving his right to make an argument in the case.
Mr Lavery said when the lawsuit was filed last year that Tommy's "shed" was a state-of-the-art $150,000 (€120,000) facility, and that the chimp had been on a waiting list for a primate sanctuary for three years.
An appeals court in Rochester in December will hear a similar case from Mr Wise involving a chimp named Kiko.
State judges dismissed both cases but allowed Mr Wise to create the record necessary for an appeal.
Mr Wise is using a legal mechanism traditionally filed on behalf of people, usually jail inmates, who claim they have been unlawfully imprisoned.
Although there are hundreds of captive chimps in the US, Mr Wise said he thought Tommy and Kiko would make compelling subjects because they lived alone in conditions he said were clearly unfit for a chimp.
The attempt to secure legal rights for animals has been criticised by some prominent legal experts, including US Circuit Judge Richard Posner and New York University law professor Richard Epstein.
