Growth hormone (GH) structure is stabilised by two disulphide bonds, C53-C165 and C182-C189 in human GH. Researchers have investigatedthe role of these structural features since the late 1960s. Early studies implied that the disulphide bonds would not be importantfor biological activity of GH. However, more advanced techniques, as well as clues from patients carrying mutations in their GH1 gene,have demonstrated that the integrity of the disulphide bond between cysteines C53 and C165 is required for biological activity of GH.In contrast, disruption of the C-terminal disulphide bond (C182-C189) has only modest effects on the biological potency of GH, despitedecreased binding affinity to GH receptor and reduced stability as shown by a comprehensive in vitro study.To confirm these results, we generated transgenic mice that express a human GH analogue, C189A, and observed normal growth-promotingand lipolytic activities. In this article, we present new data and review old results concerning the disulphide bonds of GH. We also discussrelevant mutations found in patients with growth disorders.