1. Plasma histamine and serum neutrophil chemotactic activity (S-NCA) were measured in ten atopic asthmatic patients on four separate occasions after allergen bronchial provocation testing (BPT).

2. Single doses of inhaled sodium cromoglycate (SCG; 20 mg), clemastine (0.5 mg), ketotifen (0.5 mg) and isotonic saline (0.9% NaCl) placebo were administered 30 min before bronchial provocation testing in random order and double-blind.

3. The airflow obstruction after BPT was monitored by measurement of forced expiratory volume in 1s (FEV1). Plasma histamine was measured by the double-isotope radioenzymatic assay and S-NCA by a modified Boyden chamber technique.

4. A highly significant decrease in FEV1 after BPT occurred on the placebo pre-treatment visit (P < 0.001). Prior administration of inhaled SCG, clemastine and ketotifen significantly reduced the decrease in airflow obstruction seen after BPT when compared with placebo treatment (P < 0.01, P < 0.02, P < 0.05 respectively).

5. No significant alteration in plasma histamine was detected during allergen-induced airflow obstruction.

6. Levels of S-NCA were significantly higher 5, 10 and 15 min after BPT when compared with the pre-challenge level (P < 0.01, P < 0.01, P < 0.001 respectively). These levels were not significantly decreased when airflow obstruction was inhibited by the prior inhalation of SCG, clemastine or ketotifen.

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