To further reduce the risk of transmission of COVID-19 and enhance the safety of staff, the National Institutes of Health is shifting all non-mission-critical laboratory operations to a maintenance phase. Beginning on Monday, March 23, only mission-critical functions within NIH research laboratories will be supported. Mission-critical functions include the following: care of research participants in NIH clinical protocols that are non-elective, research directly on COVID-19, urgent public health research recommended by NIH scientific leadership, work involving significant research investments that could be lost if not continued, and protection of life, property and resources, including the care of research animals. This follows a March 13 guidance to all eligible NIH staff to telework to the maximum extent possible.