The paper describes the effect of 10-, 50-, 100-, 200-, 300-, 400-, and 500-fold excess of low-molecular weight, linear, hexamethyldisiloxane (L-2) and cyclic hexamethylcyclotrisiloxane (D-3) with respect to fibrinogen (Fbg) on the conformational stability of Fbg during a 60-h incubation at 37 degreesC. This study used SPE/HPLC/UV and fluorescence of a tryptophan located in the domain of Fbg and fluorescence of 1,1'-bis(4-anilino)naphthalene-5,5'-disulfonic acid (ANS) spectroscopy. The fact that the decrease in fluorescence intensity of siloxane-treated Fbg was accompanied by red shift in the maximum wavelength indicated that denaturation of Fbg had taken place. The differences (the decrease in peak height and the shift in retention time) in chromatograms between control Fbg and siloxane-treated Fbg indicated the adsorption process of Fbg on the surface of siloxanes. Incubating hexamethyldisiloxane with Fbg at L-2-to-Fbg ratios >300 for 20 h yielded white and mould-like precipitates of Fbg. The same phenomenon demonstrating massive denaturation and aggregation was observed for a greater than 500-fold excess of D-3 with respect to Fbg after 20 h of incubation.