The blood of 107 patients undergoing venography for suspected deep vein thrombosis (DVT) was tested for D-Dimers using enzyme immunoassay (EIA) and two latex agglutination techniques. D-Dimer levels by EIA were raised in 88% of patients with proven DVT. However, levels detected with the two agglutination tests were much less sensitive, being raised in only 43% patients with DVT. A more sensitive rapid screening test is needed to provide a useful non-invasive test for the exclusion of DVT.