In response to Hurricane Katrina's extensive destruction and related public health threats, the Centers for Disease Control and Prevention (CDC) deployed more than 1,000 staff to its emergency operations center and to affected areas. Among them were members of CDC's Emergency Communication System. This paper describes the strategies and tactics used by health communication specialists during the pre-event, response, and post-event stages to address a range of emergency communication exigencies. It highlights three difficult challenges for CDC communication specialists during Hurricane Katrina: rapid dissemination of health messages; adaptation of health messages for diverse audiences, locations, and circumstances; and phasing of key risk messages during the emergency response.