BACKGROUND: The purpose of this study was to investigate the relationship between depression and heart rate variability in the thirties male workers. METHODS: Subjects were 85 thirties male workers who had routine health examination from June to July in 2002. They were classified as the depressed group (n=15) or the non-depressed group (n=70) on the basis of Zung Self-rating Depression Scale (SDS) index. 5- minute electrocardiographic (ECG) recordings were analyzed with time and frequency domain methods of heart rate variability (HRV). Standard Deviation of NN intervals (SDNN), Root-Mean-Square of Successive Differences (RMSSD), Total Power (TP), Low Frequency (LF: 0.04~0.15 Hz) power, High Frequency (HF: 0.15~0.4 Hz) power, LF/HF ratio were used as the indices of HRV. The data were analyzed using SPSS 11.0/PC program. RESULTS: There were no significant differences among the groups in drinking, smoking, body mass index (BMI), or exercise. Heart rate variability (SDNN, rMSSD, TP, LF, HF) was significantly lower in the depressed group than in the non-depressed group. Mean heart rate was also higher in the depressed group compared with the non-depressed group, but these differences did not attain statistical significance. CONCLUSIONS: The association of depressed mood with reduced heart rate variability in the thirties male workers reflect dysregulation of cardiac autonomous control and may explain their increased risk for cardiovascular disease. However, we should confirm those effects through the well-designed prospective study.