Methacholine bronchial challenges (MBCs) have been used as an important diagnostic and management tool for physicians who treat children with chronic asthma. Despite this, children less than 5 years of age present significant diagnostic and management questions that can not easily be answered because of their inability to perform standard spirometry, and thus methacholine bronchial challenges. The present study was designed to evaluate with methacholine bronchial challenge small children (between 2 and 6 years of age) with the diagnosis of or a suspected diagnosis of asthma, utilizing a new method of evaluating airflow in small children through sound analysis, Computer Digitized Airway Phonopneumography (CDAP). There were 23 children in the study between the ages of 2 and 6 years with suspected asthma who could not perform pulmonary function tests. A control group consisting of 12 subjects between the ages of 8 and 38 years of age with a history of chronic cough and/or wheezing who could perform pulmonary function tests was also studied. Of the 12 patients over the age of 8 who had MBC, 11 of them had positive challenges with a fall in FEV1 of 19% or greater. The percent change in sound intensity levels from baseline range from 232% to 396% of baseline. There was greater than 200% change in mean intensity levels with a concentration of methacholine that produced a 19% fall in FEV1 in all of the eleven patients. For one individual who had a negative MBC there was only a 16% change in pulmonary function at 25 mg of methacholine with essentially no change in sound intensity level from baseline.(ABSTRACT TRUNCATED AT 250 WORDS)