The Dimertest Enzyme Immunoassay has been used to compare the degree of thrombogenicity of the standard knitted Dacron prosthesis (n = 10) and the gelatin-impregnated Dacron prosthesis (n = 10) after infrarenal aortic reconstruction. After surgery there was a similar rise in cross-linked fibrin degradation products with both types of prostheses. Although on the third day the D-Dimer level in the gelatin-impregnated prosthesis was lower, there was no significant difference in the D-Dimer level at six weeks. This suggests that the potential risk of thrombogenicity in the gelatin-impregnated prosthesis is similar to the standard preclotted type.