Abstract The adsorption of baboon fibrinogen from buffer to glass, silicone rubber (SR), polyethylene (PE), and polystyrene (PS) was measured after 2 h at 37°C using 125I-labeled fibrinogen. Adsorption was greatest on PS (∼550 ng/cm 2) followed by PE (∼480 ng/cm 2), SR (∼440 ng/cm 2), and finally glass (∼240 ng/cm 2). The strength of attachment of fibrinogen to these materials was also examined by measuring the elutability of preadsorbed fibrinogen molecules by undiluted plasma as a function of adsorption time. Much of the fibrinogen adsorbed for only 1 min to SR, PE, and PS was displaced by plasma whereas only a small fraction of the fibrinogen adsorbed for 1 h could be displaced from these materials. On glass, practically all of the preadsorbed fibrinogen was displaced from the surface by plasma, independent of the adsorption time. The conversion or transition of adsorbed fibrinogen molecules from a weakly bound (displaceable) to tightly bound (nondisplaceable) state occurred most rapidly on PS followed by SR and PE. Estimates for the fibrinogen transition and displacement rate constants were evaluated from experimental data. A model describing fibrinogen adsorption from plasma was developed and solved analytically. The model predicts maxima in fibrinogen adsorption from plasma as both a function of contact time and plasma dilution on each of the materials studied and so appears to account for the presence of a Vroman effect as well as its variation with substrate surface chemistry.