Monsanto, which last year tried and failed to engineer a $40 billion-plus takeover of Switzerland's Syngenta (SYT) , said it has "received an unsolicited, non-binding proposal" from the Leverkusen, Germany company.
It said Bayer's proposal is subject to due diligence, regulatory approvals and other conditions.
"The board of directors of Monsanto is reviewing the proposal, in consultation with its financial and legal advisors. Monsanto will have no further comment until its board of directors has completed its review," it said.
In its own short statement, Bayer said the two sets of executives had already met. Monsanto is led by chairman CEO Hugh Grant, while Bayer's management board chairman is Werner Baumann.
"The proposed combination would reinforce Bayer as a global innovation-driven life science company with leadership positions in its core segments, and would create a leading integrated agriculture business," Bayer said.
Jim Cramer, TheStreet's founder and portfolio manager of Action Alerts PLUS portfolio, said the deal may be doomed before it really gets off the ground.
"[The antitrust department is] motivated... They don't like deals. They don't want deals on their watch," Cramer said adding that the antitrust department will likely break up Bayer and Monsanto's deal because of their client overlap.
"Bayer provides a lot of seed and crop protection to farmers, so does Monsanto," Cramer said. "That's overlap."
Shares in the maker of the Roundup weed killer closed marginally lower in New York on Wednesday at $67.13. Monsanto's stock has drifted down about 17% in the past year. At the current price it has a market value of $42.4 billion.
Bayer had slipped 3.5% on Wednesday to €92.85. The stock is down about 29% on the year and was worth €79.6 billion ($89.3 billion) as of Wednesday's close.
Last month it missed consensus expectations for the first quarter because of disappointing performances at its crop science and consumer health units.
The German company, which invented Asiprin, is seen likely to shed assets including potentially its animal health or plastics unit to help fund the acquisition if a deal materializes.
The takeover move comes amid a wave of consolidation in the crop science sector. Syngenta earlier this year agreed to a Sfr44.6 billion($45.2 billion) bid from China National Chemical Corp., following discussions with several peers and after rivals Dow Chemical (DOW) and DuPont (DD - Get Report) agreed on a complex $130 billion fusion. Of the major chemicals companies with crop science interests Germany's BASF (BASFY) , which held talks with Syngenta, is now conspicuously without a potential partner.
Like the abortive Monsanto/Syngenta combo, which the Swiss target rejected in part because of antitrust issues, a fusion of Monsanto with Bayer will receive close regulatory scrutiny
Monsanto is taking advice on the proposal from Morgan Stanley and Ducera Partners, with legal advice coming from Wachtell, Lipton, Rosen & Katz.