Two workers at Dounreay are undergoing tests following concerns they have been exposed to a radioactive metal.
The two workers from Dounreay are waiting the results of tests
The checks follow the results of routine biological samples taken from individuals who work in the nuclear site's fuel cycle area.
One works for site operator the United Kingdom Atomic Energy Authority and the other for a contractor.
A Dounreay spokesman said it could take some time before follow-up test results for plutonium were known.
The suspected intake of plutonium has been reported to the Nuclear Installations Inspectorate of the Health and Safety Executive.