Nanotechnology stocks in the United States have held up well in the past two months — unless, that is, they had the misfortune to be associated with silver nanoparticles.

Shares in Nucryst Pharmaceuticals — a company based in Wakefield, Massachusetts, that uses such particles in its popular wound dressings — took another hammering after the US Environmental Protection Agency (EPA) said it would regulate washing machines that used silver nanoparticles to kill germs (see Nature 444, 520; 2006). Nucryst uses such particles in unrelated applications. But its shares — already sharply down after a failed September dermatology trial — took a tumble late last month and are now trading at a quarter of their summer high.

The Lux Research index, which contains a basket of stocks producing and using nanotechnology, has nonetheless held steady. Peter Hebert, chief executive of New York-based Lux Research, which compiles the index, says that despite a weakening US economy, corporate investment in nanotechnology continues to expand. He adds that the EPA ruling has been misinterpreted and won't hurt nanotech as a whole.

The end of the year saw better showings by Flamel Technologies of Lyon, France, whose shares surged after the US Food and Drug Administration approved a GlaxoSmithKline heart drug delivered using Flamel's microparticle system, and have almost doubled to $32 since the summer. And shares in Oregon-based FEI, which makes scanning electron microscopes, rose sharply in November on good quarterly results.