Eight patients with asthma in remission were treated for 4 wk with a regular beta 2 stimulant. (salbutamol, 200 microgram) given 4 times/day by aerosol. Histamine provocation tests were performed at the beginning and at the end of the treatment period, and again 2 wk after cessation of treatment. Throughout the 6-wk period, the patients recorded peak expiratory flow (PEF) at home twice daily before and after inhaling 200 microgram of salbutamol. No significant differences were seen in the average PEF values or in the bronchodilator responses. There were no changes in the bronchial sensitivity to histamine during the study, and the protective effect of inhaled salbutamol against histamine provocation was preserved after the period of regular therapy. The results suggested that the regular use of a selective beta2 stimulant by inhalation in conventional therapeutic amounts in patients with asthma is unlikely to produce clinically important tolerance or increased susceptibility to an asthma-provoking stimulus.