Chiron Corp. said its board rejected an all-cash takeover offer from Novartis AG, saying the offer is inadequate.

In a statement issued on Monday, Chiron acknowledged that over the ten years since Novartis has been Chiron's largest stockholder, the two companies have regularly discussed a number of strategic initiatives, including mergers, significant acquisitions and other transactions, including transactions initiated by Novartis.

"As a result, Chiron has had an on-going dialogue with Novartis regarding its intentions with respect to its investment in Chiron," said the statement. But, Chiron said its "independent directors have not, however, solicited an offer to buy Chiron."

The statement added that after a thorough analysis and consideration of Novartis' offer, its independent directors determined that the offer is inadequate.