Objective To investigate the relationship between smoking and insulin resistance in non-obese male patients with CAD. Methods 414 consecutive non-obese male patients with angiographically-documented CAD(luminal diameter narrowing>50%)were recruited,including 113 nonsmokers and 301 smokers.With 99 miht smokers(<400 packs/year),95 medium smokers(400-799 packs/year)and 107 heavy smokers(≥800 packs/year).Insulin resistance index(IRI)was expressed by homeostasis model assessment for insulin resistance(HOMA-IR)calculated by the formula of[fasting serum glucose(mmol/L)×fasting plasma insulin(mU/L)]/22.5.IRI≥2.69 was defined as insulin resistance,while IRI<2.69 was insulin sensitive.Fasting glucose,fasting insulin and IRI were recorded and odds ratio for the incidence of insulin resistance was calculated.Results Fasting glucose was higher in heavy smokers (5.86 mmol/L)than that in nonsmokers(5.51 mmol/L,P=0.037)and mild smokers(5.33 mmol/L,P=0.014).Fasting insulin and IRI were also significantly higher in heavy smokers(10.25 mU/L)than those in non-smokers(8.72 mU/L,P=0.0231,respectively)and mild smokers(8.67 mU/L,P=0.023 1).Compared with nonsmokers,the odds ratio for the incidence of insulin resistance was 1.53(95%CI 0.55-2.94;P=0.027)in medium smokers and 1.89(95%CI 0.49-3.14;P=0.018)in heavy smokers.Conclusions The relationship between smoking and insulin resistance is highly dose dependent in non-obese male patients with CAD.