Five defence staff have been stood down after claims they used an unknown substance while deployed in Fiji.
New Zealand Defence Force was investigating the incident alleged to have happened yesterday, a spokesperson said.
It has not confirmed whether the unknown substance was an illegal drug.
A spokesperson said the five have been stood down from normal duties during the investigation, but it had not affected the defence force's humanitarian operation in Fiji.
About 400 defence force staff, including soldiers, engineers, aircrew and medics, are still in Fiji helping in the aftermath of Cyclone Winston.
The defence force said it would not make any further comment while its investigation was proceeding.