The present invention relates to a simple method for generating antibody-based structures suitable for in vivo use. In particular, the invention relates to a method for the generation of antibody-based structures suitable for in vivo use comprising the steps of: (a) selecting an antibody single variable domain having an epitope binding specificity; and (b) attaching the single domain of step (a) to an effector group. Uses of molecules generated using the method of the Invention are also described.