OBJECTIVE: The aim of the present study was to address the effect of n-3 polyunsaturated fatty acids (PUFAs) on heart rate variability (HRV) in patients treated with chronic hemodialysis. DESIGN: We performed a randomized, placebo-controlled intervention trial. SETTING: The study took place at two hospital-based dialysis centers. PATIENTS: Thirty patients with documented cardiovascular disease who were treated with hemodialysis for at least 6 months were included. INTERVENTION: Treatment consisted of 1.7 g of n-3 PUFA or a control treatment (olive oil). MAIN OUTCOME MEASURE: The outcome measure was 24-hour Holter recordings with time domain HRV measurements at baseline and after 3 months of treatment. Blood samples were obtained to assess the content of n-3 PUFA in serum phospholipids before and after treatment. RESULTS: n-3 PUFA did not significantly affect time domain parameters of HRV, compared with a control group. CONCLUSION: We conclude that treatment with n-3 PUFA does not increase HRV in patients treated with chronic hemodialysis, a result that may have been compromised by a small sample size.