SHANGHAI: Punting drug companies' stocks, though in vogue these days in the backdrop of the H1N1 flu pandemic, is definitely not for the faint hearted.

A case in point - the roller-coaster ride of the share price of Shenzhen Neptunus Bioengineering Co in the past few weeks.

The vaccine maker's shares traded on the Shenzhen bourse tumbled 12 percent for three consecutive trading days and, for unexplained reasons, bounced back nearly 4 percent yesterday to 9.05 yuan apiece.