In the present work, dynamic aspects of the interaction between fibrinogen and three model polyelectrolyte-complex (PEC) surfaces (one negatively charged, one neutral, and one positively charged) were investigated, the static aspect having been studied previously [Schmitt et al. J. Colloid Interface Sci. 92, 25 (1983)]. The method consists of carrying out preliminary adsorption with radiolabeled fibrinogen and subsequently exposing the surface to a solution of nonlabeled fibrinogen. The radioactivity of the surface is followed continuously as a function of time and, in this way, a precise time dependence of the solution—surface exchange process is obtained. It was shown that in the pseudoplateau region of the isotherm, exchange between solution and interface takes place at two significantly different rates, so that three populations of adsorbed fibrinogen have to be considered: nonexchanging, rapidly exchanging, and slowly exchanging. Lower on the isotherm a single rate of exchange was observed for the negatively charged and neutral surfaces. This rate was similar to that of the slow exchange process occurring at higher concentration. For the positively charged surface, two distinct exchange processes were observed at low as well as at high concentration. No obvious correlation could be found between exchange behavior and the varying characteristics of the different PEC surfaces, namely, charge and hydrophobicity. Taking the present results together with those published previously [Brash et al. Trans. Amer. Soc. Artif. Int. Organs 20, 69 (1974); Brash and Samak, J. Colloid Interface Sci. 65, 495 (1978)] it is possible to claim as a general rule that the “equilibrium” between an adsorbed protein layer and its solution is only partly reversible, since we find that part of the surface layer is exchangeable and part is not. It is worth noting that this conclusion emerges from experiments conducted over a wide range of time intervals: hours (this work with fibrinogen) versus days [Brash and Samak, J. Colloid Interface Sci. 65, 495 (1978) with albumin].