1. Nine asymptomatic smokers each smoked one cigarette of their usual brand on four separate occasions.
2. The inhaled smoke volume was measured by tracing the smoke with the inert gas 81Krm. Puffing indices were recorded by using an electronic smoking analyser and flowhead/cigarette holder. The expired air carbon monoxide concentration was measured immediately before and within 5 min of finishing smoking.
3. The inhaled smoke percentage (total inhaled smoke volume/total puff volume) averaged 46% to 85% in different subjects.
4. Neither the mean inhaled smoke volume per puff nor the total inhaled smoke volume per cigarette was significantly correlated with any of the puffing indices.
5. Smokers took significantly smaller and shorter puffs, left longer between puffs and inhaled less smoke as the cigarette was smoked (P < 0.01), although the proportion of the puff which was subsequently inhaled did not change significantly.
6. There was no significant intra-subject difference in any index from one visit to another.