This invention relates to binding members, especially antibody molecules, specific for interleukin 1 receptor 1 (IL-1R1). For example, isolated binding members specific for IL-1R1 which competes with IL-1 and IL-1Ra for binding to IL-1R1 and binds Il-1R1 with a KD of 10 pM or less when measured by Kinexa™. The binding members are useful for, inter alia, treatment of disorders mediated by IL-1R1 including rheumatoid arthritis, asthma and chronic obstructive pulmonary disease (COPD).