To investigate the divergent impact of radical left and radical right parties, we use original data to gauge the effects of articulation of topics through parliamentary questions on the mainstream parties. We expect that radical parties are always asking questions related to their core issues, and that mainstream parties are also asking questions on those same issues – however, we expect that as radical parties increase their attention by asking more questions on specific topics (relative to normal amount of questions asked by them on that topic), mainstream parties after radical parties have increased their attention also increase their attention to questions related to that topic. We thereby can gauge, first, whether radical parties are successful in influencing mainstream parties, and second, whether radical parties from either the right or the left are more successful in their influence on mainstream parties (cf. Meijers 2015).