Variables obtained with the forced oscillation technique (total respiratory resistance and impedance at 2, 4 and 12 Hz) and with the forced vital capacity manoeuvre (FVC, FEV1, MMEF, MEF75, MEF50, MEF25) were used in the evaluation of the bronchial allergen challenge test in 2 groups of asthmatic children. Each method was applied in 15 provocation tests and the changes of the different variables, allowing for their respective variations, were compared with the clinical assessment. Agreement with the clinical evaluation was found in 15 of 15 occasions with the forced oscillation technique and in 12 of 15 occasions with the forced vital capacity manoeuvre. With the forced oscillation technique a bronchial reaction was detected in 6 of 10 patients at 1/10 of the allergen concentration that gave positive clinical signs and the single most sensitive variable was resistance determination at 4 Hz, with significant change in 5 of 10 cases. The forced vital capacity manoeuvre allowed detection of a bronchial reaction preceding clinical signs at a tenfold lower allergen concentration in 2 of 9 cases and the most sensitive variables were FEV1 and MEF25.