Acoustic analysis of cough both in the time and frequency domain has been reported using voluntary and spontaneous cough. The main aim of this study was to discover whether such analysis of capsaicin-induced cough enables differences between normal subjects to be recognized.We present data from 13 healthy subjects (with normal lung function and no history of respiratory disease) using a new method of acoustic analysis, which presents the data in three graphical forms: 1) spectrogram; 2) overall spectral energy, 3) root mean square (RMS) pressure plots.Using the RMS sound pressure traces, different subjects had either two peaks, a single peak or multiple peaks. The occurrence of single and multiple peaks has previously been associated with disease states but we found them in normal subjects. The number of peaks and the visual pattern of the spectrogram was reproducible within and specific to each individual over time. During a peal of coughs in a single expiration, the peak amplitude of successive coughs decreased as lung volume reduced. Despite similarities in the overall spectral energy between individuals, there were marked differences in the small visual details of the spectrograms. However, in an individual, these small details were remarkably constant both within and between days, and can be regarded as a "cough signature".This type of spectrographic analysis provides a new approach to the analysis both of normal and abnormal cough sounds, and has identified similarities and differences in capsaicin-induced cough in normal individuals. It has potential as a tool with which to study the pathophysiology of cough. Eur Respir J., 1997; 10: 202-207 Cough is a powerful response to the stimulation of sensory nerves predominantly in the larynx, trachea and central airways. It is characterized by an initial contraction of the expiratory muscles against a closed glottis, followed by a violent expiration as the glottis opens suddenly [1]. In healthy subjects, cough is infrequent, is usually nonproductive, and is self-limiting. However, in patients with chronic chest disease, particularly when associated with cigarette smoking, cough is a very common and troublesome symptom [2,3]. The sensitivity of the reflex can be tested by inhaling a tussigen. One such agent is the extract of red pepper, capsaicin, which when inhaled at low concentrations produces both doserelated and reproducible coughing [4].Cough produces an easily recognizable sound, which can be recorded and used to count the number of coughs [3,5]. However, there has been little work published on the acoustic analysis of the cough sound [6,7]. In this study, we describe a method of analysing cough sounds using techniques usually employed for lung sound analysis [8], and apply this method of analysis to capsaicin-induced cough.Previous studies have shown that cough in normal individuals can be distinguished from cough in disease states [6]. This suggests that there is considerable similarity between the acoustic features of cough in normals. Anecdota...