The relationship between financial supervision and criminal law investigations is complex. How it is given shape exactly, differs from one country to another. National differences may have an impact on transnational cooperation. Whereas in transnational cases requests for mutual administrative assistance are necessary for administrative law purposes, for criminal law enforcement purposes requests for mutual assistance in criminal matters are needed. Do these different regimes for transnational cooperation pay due respect to national differences in law enforcement? To answer this question, the legal systems of Germany and the Netherlands are explored against the background of the EC Market Abuse Directive. Some alternatives for the current interstate practice are subsequently explored.