The isolation of pluripotent human embryonic stem (ES) cells at Johns Hopkins University and the University of Wisconsin has generated both excitement over the medical potential of ES cells and ethical debate over research involving them.

Amidst this discussion, VistaGen Inc. has become one of the first companies to develop a commercial application for such cells: high throughput compound screening to provide an early determination of therapeutic index - a measure of a compound's value derived from both toxicology and efficacy - in an in vitro system that is relevant to human physiology.