During the three and a half year covering the period 1989-1992, thanks to the support given by COMAC/BME/EEC for a Concerted Action on Positron Emission Tomography new developments in this field and in interlaboratory collaboration were made possible. Up to nearly 30 PET Centres participated in the programme which was both methodological and clinical. The main results were the following : In Instrumentation and radiochemistry intercomparison of technics, standardizations and protocols led to general agreements allowing comparable results to be obtained. This is particularly important since in the future various centres will work with common clinical protocols. The modelling approach has led also to interesting results in comparing the various methods of measuring cerebral and myocardial blood flow and in studying the effect of tissue heterogeneity on the accuracy of biological parameters estimation.

In Neurology and Cardiology multicentre studies of FDG metabolism in Alzheimer's disease and myocardial viability in coronary artery disease were established. The preliminary results obtained demonstrate that a large scale programme at the European level is possible.

In Psychiatry after an estimation of the European potential, efforts were given in psychopharmacology and brain metabolism.

Finally in Oncology which is a field of choice for the emergence of diagnostic tests the efforts were focused on the search of proliferation indicators and sugar or amino-acids metabolism as an estimation of tumour grade severity and response to treatment.

Information between Centres was provided by regular publication of a Newsletter. Special issues of scientific journals published the main results in Psychiatry and Instrumentation (J. Neural Transmission, Eur. J. Nuc Med., Amer. J. Nuc. Med., J. Med. Prog. Technol.). Publications resulting from collaboration between centres were accepted in high level scientific journals in Chemistry and Medicine (J. Lab. Cmpds. Radiopharm, Appl. Rad. Isot, J. Neuropsych.). Proceedings of workshops on the dopaminergic system, protein synthesis and radiochemistry were published by Kluwer Acad. Publ., Nuclear Medicine series. All these results indicate that a real concertation exists now between the European PET Centres and many projects for the future are the result of a common will.