Biogen is a top holding among biotech exchange traded funds (ETFs). The largest by assets include iShares Nasdaq Biotechnology (NasdaqGM: IBB), SPDR S&P Biotech ETF (NYSEArca: XBI) and Biotech HOLDRS (AMEX: BBH).
Biogen accounts for 23.2% of Biotech HOLDRS.
iShares Nasdaq Biotechnology
