['Impaired lung function and inflammation have both attracted interest as potentially novel risk factors for glucose intolerance, insulin resistance, and type 2 diabetes. We hypothesized that circulating levels of surfactant protein (SP)-A, which reflects interstitial lung injury, could be associated with altered glucose tolerance and insulin resistance.', 'Circulating SP-A concentration and metabolic variables (including insulin sensitivity by minimal model method, n = 89) were measured in 164 nonsmoking men.', 'Circulating SP-A concentration was significantly higher among patients with glucose intolerance and type 2 diabetes than in subjects with normal glucose tolerance, even after adjustment for BMI, age, and smoking status (ex/never). The most significant differences were found in overweight and obese subjects with altered glucose tolerance (n = 59) who showed significantly increased serum SP-A concentrations (by a mean of 24%) compared with obese subjects with normal glucose tolerance (n = 58) (log SP-A 1.54 +/- 0.13 vs. 1.44 +/- 0.13; P < 0.0001). Insulin sensitivity (P = 0.003) contributed independently to 22% of SP-A variance among all subjects. In subjects with altered glucose tolerance, insulin sensitivity (P = 0.01) and fasting triglycerides (P = 0.02) contributed to 37% of SP-A variance. Controlling for serum creatinine or C-reactive protein in these models did not significantly change the results.'] Is circulating surfactant protein A ( SP-A ) , a marker of lung injury , associated with insulin resistance?