Beta interferon is the first-line immunomodulatory agent approved for remitting-relapsing multiple sclerosis. Several preparations of interferon beta 1b and interferon beta 1a are available for treatment. The author reviews the publications on 13 open-label studies comparing the efficacy of interferon beta preparations. Based on current clinical data we can conclude that differences in efficacy between various preparations of beta interferon are subtle and often undetectable. Therefore, the individual patient response to particular treatment, tolerability, administration route, compliance and costs of the treatment should determine the therapeutic decision.