The adsorption at silica and methylated silica of genetically engineered derivatives of Z and its dimer ZZ, where Z is a hydrophilic synthetic IgG binding domain derived from staphylococcal protein A, was studied with in situ ellipsometry. The protein modifications consisted of introducing short peptide stretches near the C-terminus of the protein. Using this approach, oligopeptide stretches containing hydrophobic tryptophan (Trp) or isoleucine (Ile) [(AlaTrpTrpPro)n or (AlaIleIlePro)n (0≤n≤2), denoted Tn and In, respectively] were introduced in the protein. For comparison, the adsorption of the inserted peptide stretches (Tn and In), as well as of Trp and Ile oligomers, was investigated as well. Increasing the number of Trp residues resulted in an increased adsorption for both ZZTn, ZTn, Tn, and Trpn. At a given number of Trp residues, the adsorbed amount of the ZZ derivatives is larger than that of the peptides, but about the same as that of the Z proteins. Analogous although somewhat smaller effects were obtained for the Ile-derivatized proteins. These results are discussed in terms of the "block copolymer" nature of the proteins. Theoretical calculations using a mean-field lattice model for block copolymer adsorption gave a qualitative agreement with the experimentally obtained results.