By Adam Easton
BBC News, Warsaw
A European Parliament delegation is in Poland to examine claims that terror suspects were transported and detained secretly in Europe by the CIA.
The US has admitted rendition has taken place
The group of MEPs will meet one government minister, airport officials and journalists during their three-day fact-finding mission.
Similar delegations have visited the US, UK, Romania and Macedonia.
Poland was one of two states identified by Human Rights Watch as possibly having secret detention centres.
The Polish government has repeatedly denied the allegations.
European Union officials believe many governments in Europe are reluctant to investigate these sensitive and potentially embarrassing allegations.
Not much hope
The idea behind visits such as this one is to apply pressure to get governments to cooperate.
But privately the MEPs do not hold out much hope for this trip to Poland.
Only one middle-ranking government member has agreed to meet them, and only after the delegation insisted.
The MEPs will want to investigate claims by Human Rights Watch that CIA flights landed at a small airport in north-eastern Poland.
The airport is close to a base which houses the military's intelligence school.
As a close ally of the US, the Polish government admits both countries' intelligence services co-operate closely but it denies the country ever hosted a secret CIA prison.
Poland's parliament has carried out its own investigation into the claims. Its findings were never made public but the government declared itself satisfied.