A jury today is scheduled to begin hearing pitches from opposing sides, with witnesses to follow.
The stakes are high for Monsanto, which could face massive losses should a jury order it to pay out damages over the product, whose main ingredient is glyphosate, a substance some say is dangerously carcinogenic.
Dewayne Johnson, a 46-year-old father of two, says he is sick because of contact with Roundup, which he used for two years from 2012 as a groundskeeper for the Benicia school district near San Francisco, his lawyer Timothy Litzenburg told AFP.
"A major part of that job was spraying Roundup or Ranger Pro (a similar Monsanto product).... He sprayed it 20 to 40 times per year, sometimes hundreds of gallons at a time on the school properties," Litzenburg said.
In 2014, Johnson was diagnosed with non-Hodgkin's lymphoma, a cancer that affects white blood cells. No longer able to work two years later, he filed suit against Monsanto, accusing the company of hiding the dangers of its product.
A key to Johnson's case will be convincing jurors that Monsanto's pesticide is to blame for his illness.
"His case has been expedited because he currently has only a few months to live," his lawyer said.
Litzenburg says he represents hundreds of people who also say they are victims of glyphosate.
Whether the substance causes cancer has been the source of endless debate among government regulators, health experts and lawyers.
Monsanto, a company that is more than a century old, was recently acquired by Germany-based Bayer for more than $62 billion.
Founded in 1901 in St. Louis, Missouri, Monsanto made the artificial sweetener saccharin. The company began producing agrochemicals in the 1940s and now employs 20,000 people around the world and generates $15 billion in annual revenue.
Monsanto was one of the companies which produced a defoliant dubbed "Agent Orange," which has been linked to cancer and other diseases, for use by US forces in Vietnam but denies responsibility for how the military used it. The company also made insecticide DDT.
Monsanto's flagship herbicide Roundup was launched in 1976.
The company soon thereafter began genetically modifying plants, making some resistant to Roundup.
The pesticide has been accused of damaging the environment, contributing to the disappearance of bees and being an endocrine disruptor.
The Roundup trial in San Francisco, which will directly address whether product has caused cancer, is the first of its kind.
The International Agency for Research on Cancer, a World Health Organization body, has classified glyphosate, which is widely used around the world, as "probably carcinogenic." The European food safety and chemicals agencies have so far not followed suit. A US Department of Health study has suggested its toxicity is limited.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)