The profound importance of thrombosis in natural history of venous and arterial thromboembolism justifies long-term use of heparin, the best antithrombotic agent. Through the study of 88 cases concerning patients treated by subcutaneous calcium-heparin for a time from 3 months to 6 years, in several indications of venous and arterial thromboembolism, we can bring the following results: - The treatment is easily accepted when patients are inquired and trained. The doses must be adapted according to clotting assays, which do no more restrain patients than during oral anticoagulant treatment. - The frequency of hemorrhagic complications is the same than during antivitamine K treatments. - Thrombosis occur rarely during heparin therapy, but with high frequency during oral anticoagulant treatments. - Osteoporosis is a real but acceptable risk (10 p. cent) of long-term heparin prescription. - The true limit of treatment is the frequency (34 p. cent) of cutaneous hypersensibility reactions with high blood eosinophilia rate. Always mild, this reaction is related to the subcutaneous administration, and heparin is likely not the single impeached substance. These undesirable effects bind us to their thorough study, in order to obtain better tolerated drugs.