The present invention provides a domain antibody construct which binds to human TNF-α, with the construct comprising: (a) a domain antibody (dAb) which binds to human TNF-α; (b) a modified hinge region sequence; (c) a human or primate heavy chain constant region sequence having a truncated CH1 domain of not more than 20 residues, wherein the modified hinge region sequence contains either a deletion or a single amino acid substitution of at least one cysteine residue which normally facilitates disulfide bond formation between heavy and light antibody chains.