The invention relates to anti-TNFR1 polypeptides and antibody single variable domains (dAbs) that are resistant to degradation by a protease, as well as antagonists comprising these. The polypeptides, dAbs and antagonists are useful for as therapeutics and/or prophylactics that are likely to encounter proteases when administered to a patient, for example for pulmonary administration, oral administration, delivery to the lung and delivery to the GI tract of a patient, as well as for treating inflammatory disease, such as arthritis or COPD.