The German government condemned the experiments Monday, and Volkswagen sought to distance itself from them, with its chairman saying that "in the name of the whole board I emphatically disavow such practices."
The tests reportedly were commissioned by a research group funded by major German automakers.
Revelations of the tests add a twist to the German auto industry's attempt to move past Volkswagen's scandal over cheating on diesel tests and the resulting questioning of diesel technology across the industry.
Volkswagen Chairman Hans Dieter Poetsch said tests were "totally incomprehensible" and must be "investigated completely and without reservation," the dpa news agency reported.
A report by the New York Times found that a research group funded by major German auto companies commissioned experiments in which one group of monkeys was exposed to diesel exhaust from a late-model Volkswagen, while another group was exposed to fumes from an older Ford pickup.
