The single-breath nitrogen test, mortality, and cancer. The relationship between indices of the single-breath nitrogen test and mortality, overall cancer incidence, and respiratory cancer incidence was examined in a cohort of 876 men, 46 to 69 yr of age, examined in 1974 and followed until June 1985. Closing volume, closing capacity, and slope of phase III were not related to mortality or cancer. In contrast, FEV1 was related to mortality, with an estimated relative mortality risk of 1.37 (95% confidence interval, 1.11 to 1.70) per liter under the expected FEV1, given height, age, and smoking, but FEV1 was not related to cancer. Inability to perform acceptable single-breath nitrogen test tracings was related to mortality with a relative mortality risk of 2.03 (1.45 to 2.85), but not to cancer. We conclude that indices of the single-breath nitrogen test have no predictive value concerning overall mortality and cancer incidence. 