AIM: The aim of the present study was to assess autonomic activity and reactivity reflecting arousal functions in depression using heart-rate variability (HRV) and heart rate (HR) measurements. METHODS: HRV and HR were measured in drug-naive depressed (n = 22) and normal subjects (n = 47) both at rest and during task execution (random number generation). Rest activity was measured both before and after the task. Following power spectrum analysis of the heart rate trend, the high-frequency component (HF: 0.15-0.4 Hz) and the ratio of the low-frequency component (LF: 0.04-0.15 Hz) to the HF (LF/HF) were used as the parameters corresponding to parasympathetic and sympathetic activities, respectively. RESULTS: For the depressed subjects, HF was lower during the initial rest condition, was less inhibitedduring the task condition, and exceeded the initial rest level during the rest condition following the task. LF/HF was higher at rest, increased less during the task, and maintained its higher level during the rest condition after the task. HR was higher during the initial rest period and responded less to the task. CONCLUSION: The results indicate alteration not only of baseline activity but also of reactivity to behavioral changes in depression. These altered autonomic measures are possibly related to the disturbed arousal function and can be used as diagnostic measures and in clinical evaluation.