Fluticasone propionate (FP) and mometasone furoate (MF) are potent synthetic corticosteroids that are widely used as anti-inflammatory agents to treat respiratory diseases. As part of the assessment of the potential for side-effects associated with their use, their activities, not only at the glucocorticoid receptor (GR) but also at the other members of the steroid nuclear receptor family, have been compared. Cell-based functional systems were established to measure different aspects of GR function, as well as the activity at all the other steroid nuclear receptors. The effects of MF and FP on the GR were potent and indistinguishable. Neither corticosteroid showed any activity at the oestrogen receptor, while both were weak antagonists of the androgen receptor. FP was a relatively weak agonist of the progesterone receptor but MF was a very potent agonist of the progesterone receptor, giving activity at similar concentrations to those that stimulate the GR (concentration generating 50% maximal effect (EC50)=50 pM). Moreover, while FP was a weak antagonist of the mineralocorticoid receptor (concentration generating 50% maximal inhibitory effect=80 nM), MF displayed potent partial agonist activity (EC50=3 nM, 30%). Mometasone furoate is considerably less specific for the glucocorticoid receptor than fluticasone propionate, showing significant activity at other nuclear steroid receptors.