The TThread.Synchronize method is available in three overloaded versions (Delphi 2007): private class procedure Synchronize(ASyncRec: PSynchronizeRecord; QueueEvent: Boolean = False); overload; protected procedure Synchronize(AMethod: TThreadMethod); overload; public class procedure Synchronize(AThread: TThread; AMethod: TThreadMethod); overload; * The first version is private and therefore only used internally. * The second version is meant to be called from within the thread object itself. * The third is a class method to be called from outside and therefore needs the thread object as the first parameter. This parameter can be nil, though.