Germany's Bayer said the number of US plaintiffs blaming its glyphosate-based weedkillers for their cancer mushroomed to 42,700 from 18,400 in July.
This raises the stakes in the group's efforts to reach a settlement.
"This significant increase is clearly driven by the plaintiff-side television advertising spend which is estimated to have roughly doubled in the third quarter compared with the entire first half of the year," Bayer said.
"However, the number of lawsuits says nothing about their merits," it added.
The German company last year acquired Monsanto for $63 billion.
"However, the number of lawsuits says nothing about their merits," it added.
The company said it continued to be constructively engaged in a mediation process ordered by a federal judge in California.
Bayer is widely expected to eventually settle to buy itself out of the litigation wave, with analysts estimates on the future size of a settlement in a $8-$12 billion range.
Its shares have lost about 30% of their value since last August when a California jury in the first such lawsuit found Monsanto should have warned of the alleged cancer risks associated with its glyphosate-based weedkillers such as Roundup.
Bayer, which says regulators and extensive research have found glyphosate to be safe, is banking on US appeals courts to reverse or tone down the first three court rulings that have so far awarded tens of millions of dollars to each plaintiff.
The company said its third-quarter adjusted earnings before interest, taxes, depreciation and amortisation (EBITDA) for the group rose 7.5% to €2.3 billion, in line with market expectations.
They were helped by higher sales of crop protection chemicals, seeds and consumer healthcare products.
