The paper focuses on the mandatory initiative of the parliamentary minority (opposition) to set up a parliamentary committee of inquiry, as designed for the first time in Germany by the Weimar Constitution. This model was later adopted by some new democracies of Europe such as Albania, Kosovo, Lithuania, Portugal, Slovenia; in Hungary it was abolished in 2014. However, evidence from experience shows that due to a lack of effective legal guarantees, this legal institute functions properly only in Germany. Either no inquiries are launched, or a formal setup of a committee is followed by ineffective non-activities. A key issue is therefore the availability of inquiry rights for the parliamentary opposition during the entire inquiry procedure, and not just at the initial phase. The presentation looks at the legal background and practice of the mandatory minority initiative in the above countires and also at the possible reasons why parliamentary inquiries fail.