The adoption of Regulation No. 1/2003 raises some questions as to the effectiveness of the EC antitrust enforcement rules. Different criteria may be used to ascertain whether the new regulation actually improves the current application of Articles 81 and 82 of the Treaty. To this end an assessment was carried out on the basis of two main parameters. The first concerns whether and when it is more satisfactory for the competent public authority to intervene (before or after the anticompetitive behavior has occurred). The second, regards who is in the best position to provide the public authorities with the relevant information regarding illegitimate conduct (private parties or public agents). The results of the analysis conducted seem to indicate that the reform will prove to be more efficient than the system set up by Regulation No. 17/62, although the passage from an ex ante to an ex post regime might entail some additional costs both for the undertakings under investigation and for the public authorities responsible for the correct and uniform implementation of EC antitrust law.