In 13 patients with bronchial asthma, who were on beta 2-adrenergic bronchodilator therapy, the effects of prednisolone and ketotifen on lymphocyte beta 2-adrenoceptor density and -responsiveness were investigated. The mean lymphocyte beta 2-adrenoceptor density and -responsiveness was significantly lower than in healthy controls, presumably due to the long-term beta 2-adrenergic bronchodilator treatment. Both prednisolone 100 mg i.v. and ketotifen 1 mg b.d.p.o. for 6 days rapidly improved lymphocyte beta 2-adrenoceptor function. 16 h after prednisolone and about 6 days after the first dose of ketotifen lymphocyte beta 2-adrenoceptor density and -responsiveness had risen to values within the range in normal volunteers. The improvement of lymphocyte beta 2-adrenoceptor function was accompanied by a significant increase in peak expiratory flow rate before and after inhalation of salbutamol. It is concluded that prednisolone and ketotifen may act beneficially on the recovery of beta 2-adrenoceptor responsiveness to beta 2-adrenergic bronchodilators in tolerant asthmatic patients.