On a balmy day the thermostat in Nancy Hopkins' lab in the Center for Cancer Research on the MIT campus is set to a temperature that is uncomfortably warm-for humans, anyway. It's fine for the other occupants: minnow-sized striped zebra fish that populate the plastic tanks stacked against one wall. Around here, what the fish need, the fish get. Hopkins is fervent about the fish because she believes that they will repay her with something of immeasurable value: a fundamental understanding of life and disease.

Hopkins is one of a growing number of researchers who have begun using the zebra fish as a tool for studying the developmental biology of vertebrates. It is, in some ways, a departure from her scientific roots. Hopkins grew up professionally along with the field of molecular biology, eventually learning the ways of viruses in an effort to uncover the genetic underpinnings of cancer. Now she has traded in viruses for fish-an exchange that reflects her enthusiasm for genetics and for being part of the early stages of a new discipline.