Sixteen former peacekeepers from six different countries have already died of leukemia, in what has become known as Balkan war syndrome.
Concern has grown in the past week among European countries whose soldiers have served in the Balkans.
Sixteen former peacekeepers from six different countries have already died of leukemia, in what has become known as Balkan war syndrome.
This has been blamed on the depleted uranium (DU) used in the manufacture of Nato missiles - but Nato itself insists there is no risk of contamination.
Pressure on Nato
The four-strong team visited the Klina area, in western Kosovo - where Portuguese peacekeepers operate - measuring radioactivity and taking soil samples.
The investigation comes as pressure grows on Nato from European governments over the use of depleted uranium during the conflicts in Bosnia Hercegovina and Kosovo.
The Portuguese Prime Minister, Antonio Guterres, said on Saturday he could no longer "be completely confident" in Nato assurances, while Poland has announced plans to carry out medical tests to all its soldiers in Kosovo.
Reports from Spain say at least eight cases of cancer have been reported among Spanish personnel deployed in Kosovo and Bosnia Hercegovina.
The European Union's political and security committee is expected to debate the issue in Brussels on Tuesday.
Click here to see where concerns have been reported
On Friday, Portugal began tests on 10,000 soldiers and civilians who have served in the Balkans.
Poland has announced that more than 600 of its troops in Kosovo will undergo tests, which will involve taking samples from blood and hair as well as from water and soil where troops are stationed.
The British Government is resisting calls to carry out similar tests.
Scientists who visited 11 out of 112 sites in Kosovo bombed by Nato said on Friday they had found either remnants of depleted uranium or evidence of increased radioactivity around the impact points left by the raids.
But the World Health Organisation (WHO) says it has found no evidence of increased leukaemia in Kosovo since the 1998 bombardment.
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