The past decade has seen unprecedented advances in the development of disease-modifying therapies for relapsing-remitting multiple sclerosis (RRMS), a disease that has a worldwide prevalence of two million patients. Four agents with the ability to modulate the immune system are now being widely used for RRMS. Of these, three are forms of interferon (IFN)-β [IFNβ-1b and two preparations of IFNβ-1a (Avonex®1and Rebif®)], and one is a polypeptide of four amino acids (glatiramer acetate) with a unique mechanism of action. The administration regimens for the IFNβ-1a products differ, with Avonex®being given as 30μg intramuscularly once a week and Rebif®being given as 22 or 44μg subcutaneously three times a week.It appears safe to predict that both forms of IFNβ and glatiramer acetate will remain standard treatments for MS for years to come. However, with four therapeutic options available for RRMS, selecting a single therapy is often difficult and necessitates comparisons of the agents, which can be contentious. All four agents have shown superiority over placebo in pivotal phase III trials. Three recent prospective comparative studies have indicated that IFNβ-1b, Rebif®and glatiramer acetate may be more optimal choices than Avonex®for patients with RRMS.In a pharmaceutical environment with an estimated worldwide market of $US2.5 billion annually for RRMS, comparative studies are understandably provocative, but at the same time provide meaningful information to clinicians and patients.