Pegvisomant is a pegylated analog of growth that functions as a growth hormone receptor antagonist. The drug is capable of normalizing serum IGF-I concentrations (the chief mediator of disease activity in acromegaly) in 97% of patients, and therapy is associated with significant improvements in the symptoms and signs of GH excess. Biochemical control may be achieved with pegvisomant in patients wholly or partially resistant to somatostatin analogs, and there are emerging data to suggest that the drug may be particularly suitable for patients with acromegaly and co-existent diabetes mellitus.