1. Recordings were made of the pattern of breathing during and after smoking a cigarette in 14 smokers and nine non-smokers.
2. The most consistent effect was an increase in tidal volume during smoking which reverted to baseline over 1–2 min. Changes in breath times were smaller and less consistent. Similar effects were observed with intermittent inhalations of charcoal.
3. In four subjects the tidal volume response was significantly decreased by oropharyngeal and laryngeal anaesthesia with lignocaine.
4. Filtration of particulate matter from the cigarette smoke delayed the onset of changes in tidal volume.
5. The changes probably represent an irritant response with stimulation at laryngeal or oropharyngeal level.