After a run-in period of 2 weeks, receiving a regimen of inhaled beta 2-agonists and/or theophyllines, 38 atopic patients with asthma with perennial symptoms were randomly allocated to receive an 8-week treatment of additional inhalation treatment with either sodium cromoglycate (SCG), 2 mg four times daily, and placebo beclomethasone dipropionate (BDP), or BDP, 200 micrograms twice daily, and placebo SCG. After crossover, each group received the opposite treatment for the final 8 weeks. FEV1, FVC, and provocation concentration of histamine causing a 20% fall in FEV1 (PC20) were determined monthly and peak expiratory flow (PEF) daily throughout the study. A significant increase in FEV1, FVC, and PEF (p less than 0.01) was observed after BDP treatment was started, and likewise, in the second period, an increase in both FEV1 and PEF (p less than 0.05) was observed. The total effect on logarithm-natural (Ln) (PC20), i.e., the mean effects of the two periods, was also significant (p less than 0.01). SCG, however, was most effective when it was used as the first drug, indicated by a significant increase in FVC in the first period (p less than 0.05). Neither in the first nor in the second period did SCG treatment influence the Ln (PC20) value positively, and the SCG treatment administered in the second period could not maintain the improvement in the pulmonary function (i.e., FEV1, FVC, and PEF) obtained initially with the BDP treatment. When the effect of BDP on FEV1, FVC, PEF, and Ln (PC20) was compared to the effect of SCG in the first 8-week treatment period, no significant difference was observed (p greater than 0.1).(ABSTRACT TRUNCATED AT 250 WORDS)