The immunoglobulins of the Camelidae family belonging to subclasses IgG2 and IgG3 consist of heavy chains only. The lack of light chains is caused by a point mutation in the heavy-chain gene, resulting in the loss of the splice consensus signal and the removal of the entire CH1 domain together with introns. The heavy-chains antibodies also contain longer hinge regions and conservative amino-acid substitutions in the framework regions. Despite the lack of light chains, the heavy-chain antibodies reveal normal antigen binding ability and effector functions. The heavy-chain antibodies are relatively easy to clone and possess good stability, high specificity, low molecular weight, and the ability to recognize unique epitopes. Possible areas of application of heavy-chain antibodies include their use as in vivo imaging reagents and sources of peptide-based drugs.