In the relapsing-remitting type of the disease the objective of the therapy is the reduction of relapse rate, duration and severity, as well as the delay of transition to the progressive form of the disease. Subjects' adherence to long-term therapy of MS plays a pivotal role in the optimization of therapeutic outcome and maximization of the derived clinical benefit for the treated subjects. Rebif current formulation has been developed by assessing and refining the physicochemical characteristics of existing formulations aiming at further improving product's tolerability profile. Studies performed for the assessment of Rebif have demonstrated a 3-fold reduction in injection site reactions as well as improved overall tolerability and safety profile.