Although some investigators have reported that crackles are present only in persons with lung disease, others say they also occur in normal persons. In order to clarify this difference of opinion, we determined the prevalence of crackles in 56 women without significant lung disease. The subjects ranged from 19 to 33 yr of age (mean, 21.3). They all had a FVC greater than 80% predicted and a FEV1/FVC ratio greater than 75%. None had a history of acute or chronic lung disease. During slow inspirations from residual volume, midinspiratory fine crackles were heard at the anterior bases in 35 of 56 subjects by a physician using an acoustic stethoscope, whereas a bioengineer using an 800 Hertz high pass filtered stethoscope heard crackles in 53 subjects. Crackles during tidal breathing were heard in 2 subjects. It is postulated that the crackles noted after expiration to residual volume are nonpathologic, and occur when basilar airways, which close at the end of a forced expiration, suddenly open during inspiration. Examination of the quality, timing, and anatomic distribution of the crackles in apparently normal subjects suggests that they can often be distinguished from those resulting from diseases such as bronchitis, interstitial fibrosis, and congestive heart failure.