In the treatment of rheumatic diseases such as rheumatoid arthritis (RA) or systemic onset juvenile idiopathic arthritis (soJIA), new therapies targeting pro-inflammatory cytokines have been developed. IL-6 is a pleiotropic cytokine with a wide range of biological activities including a pro-inflammatory mediator activity. Overproduction of IL-6 has been reported to be pathologically involved in the rheumatic diseases and, therefore, blockade of IL-6 actions may improve the disease. Tocilizumab, a humanized monoclonal antibody against human interleukin-6 receptor (IL-6R), inhibits IL-6 binding to IL-6R and specifically interferes with IL-6 actions. Castleman's disease is an atypical lymphoproliferative disorder caused by the overproduction of IL-6. Tocilizumab therapy improves immunological and hematological abnormalities as well as systemic inflammatory symptoms including wasting. This translational study also confirmed the pathological significance of IL-6 in the disease. RA is a representative autoimmune inflammatory disease characterized by bone and cartilage destruction in multiple joints. Since IL-6 also plays pathological roles in RA, tocilizumab therapy has been introduced to the patients with refractory disease and has shown a strong therapeutic effect. Besides Castleman's disease and RA, tocilizumab has been shown to be effective for patients with soJIA and Crohn's disease. Tocilizumab treatment is generally well tolerated and safe. Therefore, tocilizumab can be a promising therapeutic agent for the rheumatic diseases in which IL-6 overproduction is pathologically involved.