The HAL cruise ship was in Puerto Rico during the accident.
At 11:30 a.m. Thursday, HAL said two passengers were found dead inside their stateroom.
The cabin had been immediately secured, the authorities notified, including the FBI. Holland America said they were cooperating fully with the authorities and the investigation, to make the official determination on what had occurred.
Moises Quiñones, a spokesman for FBI, said authorities had been on scene investigating.
On March 29 the ship left Tampa, Florida on a 14-day Southern Caribbean voyage. Currently, ms Ryndam is in San Juan, Puerto Rico.
A spokesman for Puerto Rico Port Authority, Efraín Santiago, told the press that the cleaning staff on the vessel had discovered the deceased travelers after knocking on the stateroom's door.