The National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) at the National Institutes of Health is sponsoring an international multi-center trial to be conducted in both adult and juvenile myositis. This study will be directed and coordinated by Dr. Chester Oddis in the Division of Rheumatology and Clinical Immunology at the University of Pittsburgh School of Medicine and Dr. Ann Reed, Chair Pediatric Rheumatology, Mayo Foundation and School of Medicine at the Mayo Clinic. This study will begin enrolling subjects at the end of 2005 and will be announced on multiple websites at that time. The goal of this study is to perform a collaborative multi-center trial by adult and pediatric rheumatologists and neurologists implementing newly defined disease activity and damage measures in childhood and adult inflammatory myopathy to examine the efficacy of an investigational biologic agent. This trial will define the disease activity and damage measures and definitions of improvement established by IMACS, thereby enhancing future myositis research and the conduct of clinical trials in IIM. Through the study of this biologic agent we will seek to elucidate the determinants of disease response and non-response in juvenile and adult IIM and gain insight into the pathogenesis of these enigmatic autoimmune syndromes.