A pretreatment test of breath-holding endurance predicted end-of-treatment outcome in 56 Smokers Clinic clients (r = .44; p less than .001). The cut off points derived by discriminant analysis were 32 seconds for men and 20 seconds for women, which correctly classified 78.6% of cases. The breath-holding test might sample the type of endurance necessary to withstand the discomfort associated with cigarette withdrawal and may also be relevant to success in quitting other addictive behaviours. However, alternative explanations are possible and more data are needed.