The present study assessed the structure and intensity of the nicotine withdrawal syndrome in 30 (22 male, 8 female) heavy smokers across three experimental conditions: smoking, brief abstinence (3.5 h), and extended abstinence (18 h). Physiological variables (heart rate and blood pressure) and psychological variables (anxious and depressed mood) were examined in terms of symptom validity and as predictors of nicotine withdrawal intensity. As length of abstinence increased, heart rate and blood pressure decreased, and anxious and depressed mood increased. Only anxious and depressed mood were significant individual predictors of withdrawal intensity. The symptom structure of withdrawal did not change over time as abstinence levels increased; each symptom's contribution to nicotine withdrawal intensity remained stable throughout the first 18 h of abstinence.