Budesonid is a topical corticosteroid for application by inhalation with a high anti-inflammatory effect. 25 patients (15 women, 10 men, average age 45.3 years) with intrinsic asthma requiring corticosteroids were treated for an average of 36 days with budesonid (Pulmicort dosage aerosol, Astra Sweden) in a dose of 3 X 400 micrograms per day. The basic therapy with beta sympathicomimetics, theophylline preparations and systemic corticosteroids was continued. Changes in the plasmacortisol level (PCS) and the course of the asthma were studied under reduction of the systemic corticosteroid dosage. The mean reduction in dosage of the systemic corticosteroid achieved was almost 2/3 of the initial dosage (p 0.001). The pathologically reduced PCS at the start of the study normalized in 13 patients (52%) to values within the standard range. A significant (p 0.001) mean increase in PCS of 43% was achieved. The eosinophils in the blood underwent no significant change. The peak flow improved by a mean 26% (p 0.001) with respect to the initial values. Despite a reduction in systemic corticosteroids, the symptoms of breathlessness, coughing and expectoration improved or declined practically without exception. Apart from some temporary hoarseness and throat irritation in 5 patients, there were no undesired side effects or incompatibility.