In 1999, California adopted historic legislation requiring that specific minimum nurse-to-patient ratios be established for all units in acute care hospitals in the state. The Department of Health Services established regulations in accordance with this legislation, and the ratios were implemented on January 1, 2004. Center researchers have been examining the potential and ultimate effects of this legislation since it was passed, and have published several reports on potential and early effects of the ratios. Center faculty also were involved in research led by Linda Aiken at the University of Pennsylvania and Barbara Mark at the University of North Carolina.