Belgium pharmaceutical firm UCB is to buy Britain's largest biotechnology company Celltech for £1.53bn (€2.26bn).
The move gives UCB access to the fast-growing biotechnology market, creating the world's fifth largest biopharmaceutical company.
It will also allow a European company to tackle the traditional dominance of US companies in this field.
Göran Ando, Celltech chief executive, will become deputy CEO of UCB.
Celltech is the biggest acquisition by the Belgian group, which only branched out from heavy chemicals in the 1980s.
It decided to buy the UK company after entering talks late last year to licence the marketing rights to CDP 870, Celltech's arthritis treatment.
The biopharmaceuticals industry had sales of more than $30bn (€25.06m) last year, with gross margins of 80%, despite analysts belief that the industry is still in its infancy.
Annual growth in the sector is about 15% or double the growth rate for conventional drugs.