1. It is a clinical impression that some patients given oral corticosteroids develop a sense of wellbeing that is 'inappropriate' to improvements in physical health. This has been termed steroid 'euphoria', but unlike steroid-induced psychosis it has not been documented. 2. To test for the size and frequency of this phenomenon, 20 patients with severe chronic obstructive airways disease (mean FEV1 0.86 l) were given 30 mg of prednisolone for 14 days, after a period of placebo administration in a single-blind study. 3. Lung spirometry and arterial saturation during exercise were measured serially, together with established measures of mood state. 4. No changes in spirometry or arterial saturation during exercise were detected until 7 days of active therapy. 5. Mood state did not change during the placebo period, but small significant reductions in anxiety and depression were measured after 3 days of prednisolone and before any measurable improvement in lung function. Mood state did not then further improve, despite measurable improvements in lung spirometry. 6. This is evidence that prednisolone may produce a mild 'inappropriate' sense of wellbeing within a population receiving the drug, rather than as an occasional idiosyncratic response.