Monsanto has been ordered to pay US$289 million (NZ$439 million) to a former school groundskeeper after jury found it contributed to the man's terminal cancer.
Dewayne Johnson's lawsuit claimed the agribusiness giant's popular Roundup weed killer was linked to his disease. After three days of deliberations, a San Francisco jury awarded him US$250 million (NZ$380 million) in punitive damages and around US$39 million (NZ$59 million) in compensatory damages.
Now, his victory could pave the way for thousands of other cases alleging the glyphosate-based herbicide causes non-Hodgkin's lymphoma.
Mr Johnson was responsible for spraying Roundup as part of his job as a pest control manager, his attorneys have said. He told the court he had two accidents that left him soaked in Roundup.
The first accident occurred in 2012, and in 2014 he was diagnosed with lymphoma. His lawsuit claimed Monsanto failed to warn him about the deadly risks of its weed-killing products.
"The jury found Monsanto acted with malice and oppression because they knew what they were doing was wrong and doing it with reckless disregard for human life," said Robert F Kennedy Jr, a member of Mr Johnson's legal team, according to the Associated Press.
"This should send a strong message to the boardroom of Monsanto."
But Monsanto still denies a link between its product and cancer, and argued Mr Johnson's cancer must have started before he began his job.
"We are sympathetic to Mr Johnson and his family," Monsanto vice president Scott Partridge said in a statement after the verdict was announced.
He claimed there were "800 studies and reviews" that "support the fact that glyphosate does not cause cancer, and did not cause Mr Johnson's cancer".
"We will appeal this decision and continue to vigorously defend this product, which has a 40-year history of safe use and continues to be a vital, effective and safe tool for farmers and others," Mr Partridge said.
CNN reported in 2017 that more than 800 patients were suing Monsanto, claiming that Roundup also contributed to their cancer.