But a shift away from glowing proteins is turning out to be harder than he expected. “Maybe it's foolish,” says Tsien, an HHMI investigator at the University of California (UC), San Diego. It is rather late in his career, he admits, to delve into an unfamiliar clinical problem. The impact of his work makes it easy to see why he feels like he's swimming against the tide.

Illustration: Riccardo Vecchio