Response to stress is an important health risk factor. We compared several methods based on automatic speech analysis for extracting prosodic information from spontaneous speech of 19 subjects participating in a study of the effects of bupropion (a medication that increases smoking cessation rates and treats depression) on stress response in smokers. Automatically extracted mean fundamental frequency (F0), F0 variability, and the mean duration of silent pauses significantly correlate with physiological measures of stress: plasma concentration of epinephrine (adrenaline), heart rate and blood pressure. These findings indicate that automated speech analysis may be used for non-invasive stress response measurement.