Adsorption properties of polybutadiene on carbon black aggregates are investigated from several experimental approaches : weighing, n.m.r. of protons attached to chains, and swelling of mixtures, induced by good solvents of the polymer. The observed apparent law of polymer adsorption is shown both experimentally and theoretically to obey a master curve obtained by using the reduced variable defined by the ratio M(n)/Q(i) (M(n) is the number of average chain molecular weight and Q(i) is the initial amount of polymer per gram of filler). The gel-like behaviour of bridged aggregates is observed for mixtures which are swollen by a good solvent, after eliminating free chains; the transverse relaxation process of protons attached to chains provides an insight into properties of the adsorbed layer.