Studies of the adsorption of immunoglobulin G (IgG) and insulin onto modified silica particles are reported. The silica particles were functionalized with the so-called thiophilic and with other groups designed to promote the specific adsorption of IgG and insulin according to thiophilic interactions. Porous silica beads were first coated with dextran which had been substituted with a calculated amount of positively charged diethylaminoethyl (DEAE) functions. This treatment was designed to “passivate” the silica, i.e. to minimize non-specific protein adsorption via the silanol groups. The DEAE-dextran coated silica was functionalized with β-mercaptoethanol via the coupling agent divinylsulfone. Ligand consisting of cysteine methyl ester residue was also coupled to the passivated silica to provide related chemical functions. The performances of the supports grafted by cysteine methyl ester and β-mercaptoethanol were studied by high-performance liquid affinity chromatography (HPAC). The support functionalized by cysteine methyl ester appears significantly more selective than the support grafted by β-mercaptoethanol. This new support, functionalized by cysteine methyl ester, showed similar adsorption characteristics as the thiophilic adsorbent. The two affinity supports allowed a one-step separation of the insulin and IgG subclasses from a pancreatic extract and mouse ascitic fluids, respectively, by HPAC. The use of this new thiophilic adsorbent thus enabled us to exploit this support in affinity chromatography and to develop a new method for the purification of insulin and IgG.