A security guard at Washington's Walter Reed Army Medical Center, a major US military hospital, fired gunshots at another guard during an argument, police said.
No one appeared to have been injured in the incident on Wednesday and the guard who did the shooting was arrested, local police spokesperson Hilton Burton told the US media.
Burton said the guard fired between six and 10 shots from his weapon.
The two guards are employed by Vance Security, a private firm founded by Charles Vance, ex-son-in-law of former president Gerald Ford.
Walter Reed treats both veterans and active-duty military personnel, many recently returned from the Iraq war.
Celebrities and top government officials - including President George W Bush and members of Congress - frequently visit soldiers recovering at the facility.