This is a 4 month open trial with TNF-blockade using infliximab (an antibody that blocks TNF) in adult patients with chronic myositis (polymyositis, dermatomyositis, inclusion body myositis) who have persisting muscle weakness and inflammatory active disease despite adequate treatment with immunosuppressives either currently or previously.||Infliximab is given as infusions, 5 mg/kg body weight, these infusions are repeated after 2, 6 and 14 weeks. The study involves 15 adult patients.||Primary outcome measure is muscle function assessed by muscle function index score.||Other outcome measures are Myositis Disease Activity core set: Patient's global assessment and physicians global assessment on visual analogue scales (VAS). Manual muscle test, Health assessment questionnaire (HAQ), serum levels of CPK, LD and extra muscular disease activity score. Muscle biopsy, Magnetic resonance imaging (MRI) of thigh muscles and Health related Quality of life, measured by SF-36.