BACKGROUND Polymorphonuclear neutrophils (PMNs) represent the first line of cellular defences in the gingival crevice. Smoking, as probably the most important environmental risk factor for periodontitis, has been shown to adversely affect many neutrophil functions. OBJECTIVE The aim of this study was to investigate the influence of smoking on PMN numbers and function in periodontally healthy smokers and non-smokers. METHODS Sixty subjects were recruited: 15 non-smokers, 15 light smokers (< 5 cigarettes/day), 15 moderate smokers (5-15 cigarettes/day) and 15 heavy smokers (> 15 cigarettes/day). Full mouth plaque index, sulcus bleeding index and probing depths were measured. Crevicular washings were obtained from all subjects to harvest PMNs. Numbers of PMNs, percentage viability, and percentage phagocytosis of opsonized Candida albicans were recorded. RESULTS Mean plaque scores and probing depths were (non-significantly) increased in smokers compared to non-smokers. Mean sulcus bleeding index scores were significantly lower in moderate (0.10 +/- 0.10) and heavy (0.07 +/- 0.11) smokers compared to non-smokers (0.14 +/- 0.13) (p < 0.05). Compared to non-smokers (1.73 +/- 1.08 x 10(6)/ml), the numbers of PMNs were higher in light (1.98 +/- 0.96 x 10(6)/ml) and moderate (2.03 +/- 1.43 x 10(6)/ml) smokers and were lower in heavy smokers (1.68 +/- 1.18 x 10(6)/ml), though there were no significant differences in PMN counts between the groups (p > 0.05). Percentage viability of PMNs was significantly lower in light (77.6 +/- 7.8%), moderate (76.5 +/- 8.2%) and heavy (75.0 +/- 6.5%) smokers compared to non-smokers (85.5 +/- 6.0%) (p < 0.05). Furthermore, the ability of PMNs to phagocytose was significantly impaired in light (58.3 +/- 4.1%), moderate (51.9 +/- 2.33%) and heavy (40.9 +/- 3.5%) smokers compared to non-smokers (74.1 +/- 4.1%) (p < 0.05), with evidence of a dose-response effect. CONCLUSIONS Cigarette smoking adversely affected PMN viability and function in this periodontally healthy population.