The author argues that risk carriers do have a moral responsibility not to expose others unknowingly to the risk of a fatal infectious disease. Risk carriers also have a moral duty to inform others who may be or may have been at risk for AIDS because of contact with the risk carrier. Not only does such a disclosure respect the autonomy and right of others to know, it also indirectly helps to protect third parties who might otherwise unknowingly be exposed to a risk of infection. The moral duty of the risk carrier to disclose the risk of infection to others, however, extends only to those actually placed at risk. The moral duties of the health care professional who treats the risk carrier are similar. The professional must preserve the risk carrier's privacy but also prevent the harm the risk carrier may cause to others. The Rock Hudson and Tarasoff cases are used as illustrations. 5 notes.