BACKGROUND: omega-3 fatty acids (omega-3 FAs) found in dietary fish or fish oils are anti-inflammatory agents that may influence Alzheimer's disease (AD). OBJECTIVE: To study the effects of dietary omega-3 FA supplementation on inflammatory markers in cerebrospinal fluid (CSF) and plasma from patients with mild to moderate AD. METHODS: Thirty-five patients (70.3 +/- 8.2 years) were randomized to a daily intake of 2.3 g omega-3 FAs or placebo for 6 months. The inflammatory markers interleukin (IL)-6, tumour necrosis factor-alpha and soluble interleukin-1 receptor type II (sIL-1RII) were analysed in CSF and plasma at baseline and at 6 months. The AD markers tau-protein, hyperphosphorylated tau-protein and beta-amyloid (Abeta(1-42)) were assessed in CSF. High-sensitivity C-reactive protein was assessed in plasma. A possible relation to the APOE genotype was investigated. RESULTS: There was no significant treatment effect of omega-3 FAs on inflammatory and AD biomarkers in CSF or on inflammatory markers in plasma, nor was there any relation with APOE. A significant correlation was observed at baseline between sIL-1RII and Abeta(1-42) levels in CSF. CONCLUSIONS: Treatment of AD patients with omega-3 FAs for 6 months did not influence inflammatory or biomarkers in CSF or plasma. The correlation between sIL-1RII and Abeta(1-42) may reflect the reciprocal interactions between IL-1 and Abeta peptides.