Prospective clinical trials on cancer started in Central and Eastern Europe in the early 70s under the auspices of the Council of Mutual Economic Assistance (CMEA). The objective of the CMEA Chemotherapy Group was to conduct prospective phase III studies with particular focus on drugs developed in the member countries. The main organizational problems were insufficient contact with the Trial Center and the excessive formalism of the cooperation. In the mid-80s most of the clinical research was taken over by the new structure: the South and East European Oncology Group (SEEOG), later renamed the Central and East European Oncology Group (CEEOG). CEEOG is a drug-oriented group consisting currently of over 30 institutions from eight countries. Its major interests have included breast cancer, ovarian cancer, lung cancer and head and neck cancer. Most of the studies have been phase II trials carried out in cooperation with various international companies. Most recently another regional cooperative group has been created: the Central European Cooperative Oncology Group (CECOG), whose main objectives are to conduct phase III studies on new chemotherapy combinations.