Baxalta was split from Baxter International in July 2015.

Shire PLC the Dublin-based biopharmaceutical company has made an offer of around $30.6 billion in stock to acquire Baxalta Inc.

Baxalta is a rare-disease treatment maker and seller, more specifically focused on bleeding disorders and immune deficiencies. The offer comes just after Baxalta completed its separation from Baxter International Inc, who however remains the biggest shareholder of the company with 24% holdings.

The partnering with Shire would mean a lower tax rate for Baxalta, a benefit which will mean their tax rate would be held at 16 to 17 percent. Currently the predicted tax rate for the company in the second half of the year is 23 to 24 percent.

Shire has said that the combining of the two companies would boost sales growth to double-digits and also boost profits in the second half of the year once the deal has been closed.

Shares in Baxalta had risen by 21% prior to the stock market opening however Shire’s stock price has fallen by around 4% in this morning’s trading.

The offer as it stands to Baxalta offers shareholders in the company a 0.1687 Shire American depositary share for each Baxalta share that they hold. Baxalta has not engaged in any negotiations with Shire with regard to the offer which was proposed in July, and in a letter to the Chief Executive of Baxalta Ludwig N. Hanston, Shire had said “you have left us with no choice but to make our proposal known to your shareholders.”

The offer would leave the shareholders of Baxalta with around a 37% hold in the new combined company and the CEO of Shire, Flemming Ornskov believes that the partnership would mean that they would become “the leading global biotech company in rare diseases,”.