Division of powers between the European Community and its Member States in the field of genetically modified organisms' regulation is a complex issue, requiring a thorough analysis of primary as well as of secondary law provisions. The revision of Community legal regime on GMO has been pointed out by the Member States as the prerequisite for putting an end to the so-called 'de facto moratorium' and for overcoming the decision-making impasse with regard to placing GMO and GM products on the EC market and their use within the Community, which is particularly important having in mind the complaints filed by the United States, Canada and Argentine and the dispute settlement proceedings initiated against the European Community and its Member States at the World Trade Organisation (WTO). However, many issues have not been resolved yet and they are a subject of intense debate at various levels (regional, state and Community). Individual Member States (as well as their regions) are exploring the possibilities under the EC law to pursue their own levels of environmental and human health protection, higher than the EC level deemed appropriate in this field, and to prohibit or restrict the free circulation and use of GMO and GM products within their territory. To determine the impact which the Community legal acts referring to GMO have on Member States' powers in this area of regulation it is essential to analyse the legal basis of the mentioned acts, their objective and content, and finally - the degree and scope of harmonization achieved at the EC level. It is essential to ensure transparency and coherence in this sensitive field of regulation and to provide balance between the fundamental objectives: establishment of high level of environmental and human health protection as well as providing smooth, undistorted functioning of the EC internal market and further safe development of modern biotechnology.