D.Dimer is currently used as a diagnotic help in thromboembolic events. The first application widely validated concerns the exclusion diagnosis of deep vein thrombosis and pulmonary embolism. In this context D.Dimer measurements must be performed individually and they must offer a good accuracy in evaluating the clinical decision threshold which is of 0.5 micrograms/ml when D.Dimer is expressed as initial fibrinogen equivalent. For this objective we report a new membrane based ELISA technique, which uses an immunofiltration device and two complementary monoclonal antibodies. The first one is coated onto the membrane and is used for the D.Dimer capture. The bound analyte is then revealed later using the second monoclonal antibody coupled to alkaline phosphatase. The assay is performed in less than 10 minutes and it can be used instantaneously by the clinical laboratories in emergency situations. Only 200 microliters of a standard citrated plasma are required. All samples containing more than 0.5 micrograms/ml D.Dimer produce a color development which intensity is a relation of the D.Dimer concentration. All specimen with levels below 0.3 micrograms/ml give negative tests, whereas a grey zone is present between 0.3 and 0.5 micrograms/ml. This assay offers all the specifications required by its applications to the exclusion diagnosis of deep vein thrombosis and pulmonary embolism.