Pegvisomant is a pegylated analogue of growth hormone (GH) that functions as a growth hormone receptor antagonist. Clinical trials of its use in acromegaly commenced in 1997; the drug was approved in the US in March 2003 and in Europe in November 2003. In the same year, it was made available on prescription in several European countries, with further launches due in 2004. Pegvisomant is capable of normalising serum insulin-like growth factor-I concentrations (the chief mediator of disease activity in acromegaly) in 97% of patients with active acromegaly, and therapy is associated with a significant improvement in the symptoms and signs of GH excess. Disease control is achievable with pegvisomant in patients who are wholly or partially resistant or do not tolerate somatostatin analogues; preliminary data suggest that the drug may be particularly suitable for patients with acromegaly and co-existent diabetes mellitus.