Cigarette smoking is the dominant risk factor for chronic obstructive pulmonary disease (COPD) but only 10-15% of smokers develop the condition. Risk does not relate closely to cumulative cigarette consumption, perhaps because smokers vary in the degree and depth of smoke inhalation. This study examined the role of smoke inhalation in the development of COPD. Eighty current smokers and 20 lifetime nonsmoking volunteers (aged 35-65 yrs) were recruited. Lung function variables were measured and high-resolution computed tomography (HRCT) scans performed. Smoke inhalation was assessed by CO boost (the increment of expired carbon monoxide 5 min after smoking a cigarette) and serum cotinine. Mean CO boost was 6.3 parts per million (ppm) in smokers with low CO transfer coefficients (KCO) and 2.9 ppm in those with normal KCO (p=0.006); 7.2 ppm in smokers with both HRCT-defined emphysema and a low KCO and 2.6 ppm in those with neither abnormality (p=0.002); 4.5 ppm in smokers with HRCT-defined emphysema alone and 2.8 ppm in those without (p=0.08). Mean serum cotinine was 328 ng x mL(-1) in smokers with chronic productive cough and 243 ng x mL(-1) in those without (p=0.005). Lifetime nonsmokers had normal HRCT scans, lung function and serum cotinine. Emphysema is associated with high alveolar smoke exposure as measured by CO boost. Productive coughing is associated with high nicotine uptake, probably from airway smoke particle deposition.