A method for the production of at least one single-chain Alphabody polypeptide, having the general formula HRS1-L1-HRS2-L2-HRS3, wherein - each of HRS1, HRS2 and HRS3 is independently a heptad repeat sequence consisting of 2 to 7 consecutive heptad repeat units, at least 50% of all heptad a-and d-positions are occupied by isoleucine residues, each HRS starts and ends with an aliphatic or aromatic amino acid residue located at either a heptad a- or d-position, and HRS1, HRS2 and HRS3 together form a triple-stranded, alpha-helical, coiled coil structure; and - each of L1 and L2 are independently a linker fragment, which covalently connects HRS1 to HRS2 and HRS2 to HRS3, respectively, and consisting of at least 4 amino acid residues, preferably at least 50% of which are selected from the group proline, glycine, serine; and having detectable binding affinity for, or detectable in vitro activity on, a viral protein of interest, said method at least comprising the steps of: a) producing a single-chain Alphabody library comprising at least 100 different-sequence single-chain Alphabody polypeptides, wherein said Alphabody polypeptides differ from each other in at least one of a defined set of 5 to 20 variegated amino acid residue positions, and wherein at least 70% of said variegated amino acid residue positions are located either: (i) at heptad e-positions in a first alpha-helix of the Alphabody polypeptides and at heptad g-positions in a second alpha-helix, and optionally at heptad b-positions in said first alpha-helix of the Alphabody polypeptides and/or at heptad c-positions in said second alpha-helix of the Alphabody polypeptides, or (ii) at heptad b-, c- and f-positions in one alpha-helix of the Alphabody polypeptides, or (iii) at positions in a linker fragment connecting two consecutive alpha-helices of the Alphabody polypeptides, and b) selecting from said single-chain Alphabody library at least one single-chain Alphabody having detectable binding affinity for, or detectable in vitro activity on, said viral protein of interest. - each of HRS1, HRS2 and HRS3 is independently a heptad repeat sequence consisting of 2 to 7 consecutive heptad repeat units, at least 50% of all heptad a-and d-positions are occupied by isoleucine residues, each HRS starts and ends with an aliphatic or aromatic amino acid residue located at either a heptad a- or d-position, and HRS1, HRS2 and HRS3 together form a triple-stranded, alpha-helical, coiled coil structure; and - each of L1 and L2 are independently a linker fragment, which covalently connects HRS1 to HRS2 and HRS2 to HRS3, respectively, and consisting of at least 4 amino acid residues, preferably at least 50% of which are selected from the group proline, glycine, serine; and a) producing a single-chain Alphabody library comprising at least 100 different-sequence single-chain Alphabody polypeptides, wherein said Alphabody polypeptides differ from each other in at least one of a defined set of 5 to 20 variegated amino acid residue positions, and wherein at least 70% of said variegated amino acid residue positions are located either: (i) at heptad e-positions in a first alpha-helix of the Alphabody polypeptides and at heptad g-positions in a second alpha-helix, and optionally at heptad b-positions in said first alpha-helix of the Alphabody polypeptides and/or at heptad c-positions in said second alpha-helix of the Alphabody polypeptides, or (ii) at heptad b-, c- and f-positions in one alpha-helix of the Alphabody polypeptides, or (iii) at positions in a linker fragment connecting two consecutive alpha-helices of the Alphabody polypeptides, and (i) at heptad e-positions in a first alpha-helix of the Alphabody polypeptides and at heptad g-positions in a second alpha-helix, and optionally at heptad b-positions in said first alpha-helix of the Alphabody polypeptides and/or at heptad c-positions in said second alpha-helix of the Alphabody polypeptides, or (ii) at heptad b-, c- and f-positions in one alpha-helix of the Alphabody polypeptides, or (iii) at positions in a linker fragment connecting two consecutive alpha-helices of the Alphabody polypeptides, and b) selecting from said single-chain Alphabody library at least one single-chain Alphabody having detectable binding affinity for, or detectable in vitro activity on, said viral protein of interest.