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When the test of bronchial provocation with inhalant allergens is performed in atopic asthmatics, we may find an immediate response (IR), a late response (LR) or a dual response (IR-LR). The immediate response occurs between 10 to 30 minutes after the allergenic exposition and it is resolved spontaneously in about one to two hours. A proportion of these patients, estimated around 47-73% presented a LR. The LR is manifested 3 or 5 hours after the inhalation test, maximum at 6-12 hours and may persist until 24 hours. The late response serves as a clinical model of asthma because the bronchial response is more prolonged and severe than the immediate response. This is best controlled with corticosteroids while bronchial reversibility is difficult with sympathomimetics only, a fact commonly observed in the natural course of asthma. The early response was observed to be in relation with multiple factors more predictable than the late response. The object of this work was to evaluate if the LR was related with factors such as the degree of obstruction previous to the test, the intensity of immediate bronchial response and the maximum dose of inhaled allergen. The present study was performed in 34 children of both sexes with ages ranging between 6 and 14 years, diagnosed with bronchial asthma caused by Dermatophagoides (26 patients), and Alternaria (8 patients) through the score of Foucard with positive bronchial provocation test with the allergen. The BPT was performed according to the method described for Cockcroft, utilizing a continuous pressured nebulizer, inhaling for two minutes at current volume. We employed the De Villbis 646 model nebulizer with flow of air at 6 l/min and output at 0.13-0.16 ml/min. The inhaled concentrations of allergen progressively increased by ten fold, in Dermatophagoides 0.01; 0.1; 1 and 10 BU/ml, and for Alternaria 1/1,000,000, 1/100,000 and 1/10,000 P/V. Ten minutes after each dose a spirometric function with pneumoscreen Jaeger was performed. If the FEV1 was decreased by 20% from the control value, we considered the IR positive. The late response was evaluated through an hourly control of the peak respiratory flow rate (PEFR) with a Mini Wright within a 24 hours period after the test, respecting nocturnal sleep. We considered positive (LR) if PEFR fall was equal or superior to 40% of the basal value and the presence of bronchial symptoms.(ABSTRACT TRUNCATED AT 400 WORDS)