Methacholine sensitivity was evaluated in 166 young subjects who had normal resting spirometric values but who presented problems suggesting lower airways hyperreactivity. Fifty-eight patients (35%) did not have significant sensitivity. The diagnosis of asthma was excluded in this subgroup. Forty-one patients (25%) had mild methacholine sensitivity, 49 (30%) had moderate sensitivity, and 18 (11%) had extreme methacholine sensitivity. Many patients who reacted had chief complaints of cough, bronchitis, or other low respiratory-tract symptoms and did not complain of wheezing. Methacholine challenge helped to clarify appropriate therapy in these individuals. One-year follow-up of these patients showed most patients to be continuing the therapeutic regimen that had been prescribed initially. Methacholine bronchoprovocation was a useful adjunct to management of this large outpatient population of children and young adults and deserves attention as a procedure relevant to patients care, not solely as an investigational test.