German automakers are apologizing for using caged monkeys in diesel exhaust testing to gauge the effects of toxic fumes.

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Volkswagen officials Monday called for an investigation into the 2014 test and "said such studies were unjustifiable," according to Reuters.

The New York Times first reported on the study last week, confirming a company called the European Research Group on Environment and Health in the Transport Sector was used by the automakers, including BMW and Daimler, to set up the tests with an American research lab.

"We believe that the scientific methods used to conduct the study were wrong and that it would have been better not to undertake it all," Volkswagen said in a statement Monday, according to CNN Money.

The testing on monkeys preceded the Volkswagen scandal in which the carmaker was caught rigging exhaust systems to pass environmental safety standards, and eventually shelled out billions of dollars for fines and other costs.

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Mathew Palmer, a former Delta Air Lines employee, at his home in Atlanta on Thursday, Oct. 9, 2025.  Palmer was fired less than two weeks after writing a post on social media about the assassination of conservative activist Charlie Kirk. (Natrice Miller/AJC)