A New York judge has granted a hearing for two chimpanzees that a lawsuit claims are being "unlawfully detained".
The unprecedented move shows that a court "could possibly" see the chimps as "legal persons", an animal rights organisation said on Tuesday.
Manhattan Supreme Court Justice Barbara Jaffe ordered Stony Brook University on Monday to show cause for holding the two chimps, Hercules and Leo, which are used for biomedical experimentation by the school, according to court papers.
Nonhuman Rights Project, the animal rights organisation that brought the case, hailed the groundbreaking decision.
They say that under New York state law, the order means that the court believes "at minimum" that the chimps could be seen as "legal person".
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"The order does not necessarily mean that the court has declared that the two chimpanzees ... are legal persons," the organisation said in a statement.
"The issue will be determined only after it is fully briefed and argued at the adversarial hearing."
If the university fails to present sufficient reason for keeping Hercules and Leo in captivity, the judge can order that the chimps be released to the care of an animal sanctuary in Florida.
