Napolitano said there is no evidence that Secret Service agents hired strippers and prostitutes while in that country last year.
The allegations surfaced after agents and U.S. military personnel were implicated in a prostitution scandal in Colombia last month. A dozen agents, officers and supervisors and 12 other U.S. military personnel were implicated in the incident, which involved a night of heavy drinking in Cartagena before President Barack Obama's visit to the Summit of the Americas. Some were accused of bringing prostitutes back to their hotel rooms.
Napolitano said she doesn't believe there's a broader problem with the agency's culture.
Meantime, House Homeland Security Committee Peter King said the Secret Service is poring over interviews with 10 of 12 women involved in the scandal, and so far there is no indication that any posed a national security threat.
King said a letter from the service stated that none of the women have any connections to any terrorist groups and none show up on any watch lists.
The Secret Service has issued only limited public statements since the April 12 incident. The service has forced eight employees from their jobs and was seeking to revoke the security clearance of another employee, effectively forcing him to resign.
Three others have been cleared of serious wrongdoing. The military was conducting its own, separate investigation but canceled the security clearances of all 12 enlisted personnel.
The service has also gone through some changes in light of the scandal. On Friday, the Secret Service announced that a chaperone would travel on all overseas trips, alcohol consumption was prohibited 10 hours before shifts and that foreign nationals were not permitted in hotel rooms.
The Associated Press contributed to this report.