In November 1994, the U.S. Department of Veterans' Affairs (VA), the Department of Defense (DoD), and the Pennsylvania Department of Health requested that CDC investigate a report of unexplained illnesses among members of an Air National Guard (ANG) unit in south-central Pennsylvania (Unit A) who were veterans of the Persian Gulf War (PGW) (August 1990-June 1991). These veterans had been evaluated at a local VA medical center for symptoms that included recurrent rash, diarrhea, and fatigue. A three-stage investigation was planned to 1) verify and characterize signs and symptoms in PGW veterans attending the VA medical center; 2) determine whether the prevalence of symptoms was higher among members of Unit A than among members of other units deployed to the PGW and, if so, whether the increased prevalence was associated with PGW deployment; and 3) characterize the illness and identify associated risk factors. This report presents preliminary findings from stages 1 and 2 (stage 3 is in progress).