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Background: Onset of wheeze is the endpoint often used in the determination of a positive bronchial challenge test (BCT) in young children who cannot perform spirometry. We sought to assess several clinical endpoints at the time of a positive BCT in young children with recurrent wheeze compared to findings in school‐aged children with asthma. Methods: Positive BCT was defined in: (1) preschool children (n = 22) as either persistent cough, wheeze, fall in oxygen saturation (SpO2) of ≥5%, or ≥50% increase in respiratory rate (RR) from baseline; and (2) school‐aged children (n = 22) as the concentration of methacholine (MCh) required to elicit a 20% decline in FEV1 (PC20). Results: All preschool children (mean age 3.4 years) had a positive BCT (median provocative MCh concentration 1.25 mg/ml [IQR, 0.62, 1.25]). Twenty (91%) school‐aged children (mean age 11.3 years) had a positive BCT (median PC20 1.25 mg/ml [IQR, 0.55, 2.5]). At the time of the positive BCT, the mean fall in SpO2 (6.9% vs. 3.8%; p =.001) and the mean % increase in RR (61% vs. 22%; p <.001) were greater among preschool‐aged than among school‐aged children. A minority of children developed wheeze at time of positive BCT (23% preschool‐ vs. 15% school‐aged children; p =.5). Conclusions: The use of wheeze as an endpoint for BCT in preschool children is unreliable, as it rarely occurs. The use of clinical endpoints, such as ≥25% increase in RR or fall in SpO2 of ≥3%, captured all of our positive BCT in preschool children, while minimizing undue respiratory distress. [ABSTRACT FROM AUTHOR]