Actelion rose 8.56% to change hands at an all-time high of Sfr215 each following a Bloomberg report that the group was in "advanced talks" with Sanofi that could lead to a $30 billion takeover.
Actelion said earlier this week it had "engaged in discussions with another party regarding a possible strategic transaction," but cautioned that there can be "no certainty at this point that any transaction will result.
The statement came after Johnson & Johnson JNJ abandoned its potential $27 billion takeover bid.
Reports have earlier linked the Allschwil, Switzerland-based group to Sanofi while merger speculation has lifted shares more than 34% since late November, when speculation for the J&J bid emerged and the New Jersey-based group confirmed its interest in the Swiss firm.
Sanofi has always been considered a potential challenge to J&J's ambitions, however, even as reports suggested that Actelion's fiercely independent co-founder Jean-Paul Clozel, who has for years resisted suggestions the company is a target, was looking at ways to keep the company at least partially under his control.
Sanofi shares were quoted 0.85% lower in Paris at €75.27 each.