The stability of lung sounds measurements over time may influence their clinical usefulness. In the present study we investigated the temporal variability of the spectral pattern of normal lung sounds. Breath sounds from five healthy men were recorded on the trachea and at four locations over the chest wall. Each subject was studied twice with a time interval of 1 wk. On each occasion, measurements were done in duplicate, with a 30-min interval between recordings. Sounds were amplified, band-pass filtered (75 to 2,000 Hz) and digitized into a computer, and the average spectra of the inspiratory, expiratory, and background sounds were calculated. The variability of corresponding spectra were calculated between the daily duplicate (same-day variability, SDV) and between the two recording sessions (between-day variability, BDV). SDV was 32.8 +/- 12.0% during inspiration and 40.8 +/- 12.6% during expiration (p = 0.005). BDV was 36.9 +/- 11.3% during inspiration and 42.7 +/- 12.7% during expiration. These values were not significantly different from SDV except for sounds recorded from the interscapular region (SR). At this location the SDV was 28.2 +/- 7.2% during inspiration and 40.8 +/- 14.2% during expiration, and the BDV was 48.2 +/- 18.7% during inspiration and 77.6 +/- 22.3% during expiration (p < 0.05). The increased BDV at SR was found to be a result of slight differences in microphone position from the first session to the next. Similar changes in microphone position at the other recording sites did not alter the variability of lung sounds.(ABSTRACT TRUNCATED AT 250 WORDS)