The regular findings of a nodular perineuritis in peripheral nerve trunks and of a nodular polymyositis in skeletal muscles indicates the systemic nature of this disease. Rheumatoid arthritis is not solely a disease of the joints but a systemic disease, characterized by a widespread distribution of a nodular lymphocytic inflammation in peripheral nerves and skeletal muscles. The new findings in the nerves and muscles offer an explanation of the generally encountered clinical manifestations of pain, tenderness, trophic changes and muscular atrophy.