The radionuclide oxygen-15, half-life 2.05 min, is used in simple chemical forms to study oxygen metabolism, blood flow and blood volume in man, using the technique of positron emission tomography (PET). The production of 15O and the preparation of [15O]O2, [15O]CO2, [15O]CO and [15O]H2O is now well established in several PET centres in Europe, North America and Japan. In order to provide a practical design and operational data base for others intending to make use of these techniques an EEC task group representing four European laboratories routinely using 15O in PET studies was set up to review the current practice of 15O production purification and quality control of the clinically useful products.