The German government has denounced experiments funded by German carmakers in which humans and monkeys reportedly inhaled diesel exhaust fumes.
German media say the health impact research was done by EUGT, a body funded by Volkswagen, Daimler and BMW.
Such tests could not be justified, the government said, demanding details. A minister called them "abominable".
Daimler also condemned them. VW is embroiled in a scandal over software that gave false diesel exhaust data.
In 2015 VW admitted having fitted "cheat" devices in the US that made their engines appear less polluting than they actually were.
EUGT was dissolved by the carmakers last year. The initials stand for European Research Group on Environment and Health in the Transport Sector.
"These tests on monkeys or even humans cannot be justified ethically in any way," said Chancellor Angela Merkel’s spokesman, Steffen Seibert.
Environment Minister Barbara Hendricks called the experiments "abominable" and expressed shock that scientists had agreed to conduct them.
Social Democrat politician Stephan Weil - a VW supervisory board member - called them "absurd and abhorrent". "Lobbying can be no excuse whatsoever for such testing," he said.
社会民主党的政治家斯蒂芬·威尔 - 大众监督委员会成员 - 称他们“荒唐可恶”。他说：“游说不能作为做这样的测试的理由。”
On Thursday the New York Times reported that the EUGT research was designed to counter a 2012 decision by the World Health Organization to classify diesel exhaust as a carcinogen.
It said that in 2014, EUGT had exposed 10 monkeys to fumes - in an air-tight chamber - from several cars, including a diesel VW Beetle. The testing took place at a lab in Albuquerque, New Mexico.
Then at the weekend Germany’s Stuttgarter Zeitung and SWR radio reported that 19 men and six women had inhaled diesel fumes in another EUGT experiment.
During a month of tests at a lab in Aachen, west Germany, they were exposed to various concentrations of diesel fumes, which contain toxic nitrogen oxides (NOx). The BBC has not seen the study itself, but German media say it was published in 2016.