The authors studied the safety and tolerability of subcutaneous interferon beta-1a at different doses in 24 children with clinically definite multiple sclerosis. After a mean treatment period of 44 months, interferon beta-1a was well tolerated in 22 patients, although two experienced possible serious adverse events. Although effectiveness cannot be inferred from this study, the authors did observe a significant reduction in the relapse rate at 22 mug, three times weekly, in the relapsing-remitting subgroup.