BACKGROUND: Many preoperative risk factors such as old age, smoking, obesity, and a history of chronic obstructive lung disease have been known to reduce lung function and to increase respiratory complications and mortality postoperatively. Each risk factor has been evaluated separately, and clinical influence of such risk factors has been reported differently according to the author or patient group. Therefore, we would like to assess each risk factors those effect on peak expiratory flow rate (PEFR) and respiratory system resistance (Rrs). In addition, we also want to evaluate the combined effects of such risk factors on PEFR and Rrs. METHODS: PEFR was evaluated in 73 patients before intubation. Anesthesia was induced with 2microgram/kg fentanyl and 5 mg/kg thiopental. Tracheal intubation was done with 1 mg/kg succinylcholine and patients were paralysed with 0.1 mg/kg vecuronium in 100% O2 and mechanical ventilation was set (frequency; 10, I: ratio; 1:, tidal volume; 10 ml/kg). Two minutes after intubation, Rrs was measured immediately following airway placement using the isovolumetric method during positive pressure ventilation with oxygen using a pneumotachography Capnomic Ultima (Datex, USA) in all patients. Rrs and PEFR were assessed by age, obesity, smoking, exercise tolerance and chronic obstructive lung disease. Patients were divided into three groups to evaluate the effect of combined factors upon PEFR and Rrs. Group 1 (n = 25) included zero to two single risk factor, Group 2 (n = 30) included three to four single risk factor and Group 3 (n = 18) included five to six single risk factor. All data was collected and analyzed with an appropriate statistical method. RESULTS:Single factor; The obesity and smoking groups showed a significant increase in Rrs (P < 0.05). The old age (above 65 yrs) and chronic obstructive lung disease groups showed a significant decrease in PEFR (P < 0.05) (Table 1). Combined factor; Group 2 and 3 showed a significant decrease in PEFR and an increase in Rrs compared to Group 1 (Fig. 1, 2). CONCLUSIONS: High risk group having 3 more single risk factors showed significant decrease of PEFR and increase Rrs simultaneously. The evaluation of preoperative pulmonary risk factors should be evaluated not by single factor but by multiple combined factors.