To examine the effect of chronic NaCl ingestion on blood pressure (BP) in the elderly, a meta-analysis was undertaken of 11 randomised controlled trials of which five included patients > or =60 years of age only and six included patients with a mean age close to 60 years. The following databases were used: Medline, Embase, Current Contents, The Cochrane Library, the AMI and IPA databases. Mean erect systolic and diastolic blood pressures (SBP/DBP) on chronic (> or =9 weeks) high and low NaCl diets were recorded, the pooled mean effect, the pooled standard error and 95% confidence intervals (Cl) were calculated and linear regression was used to evaluate the potential association between NaCl intake and BP. When all trials were pooled, a chronic high NaCl diet significantly increased mean SBP and DBP by 5.58 mm Hg (95%Cl 4.31-6.85) and 3.5 mm Hg (95%Cl 2.62-4.38) respectively. There was a significant association between the level of NaCl intake and SBP (P = 0.05, r2 = 0.37) but not DBP (P = 0.76, r2 = 0.01). When trials were pooled separately, a chronic high NaCl diet increased SBP by 5.46 mm Hg (95%Cl 3.56-7.36) and DBP by 2.63 mm Hg (95%Cl 1.18-4.08) in trials including patients > or =60 years of age only, and increased SBP by 3.27 mm Hg (95%Cl 1.23-5.31) and DBP by 2.69 mm Hg (95%Cl 1.44-3.94) in trials including patients with a mean age close to 60 years. These data suggest that a chronic high NaCl diet in elderly patients with essential hypertension is associated with an increase in SBP and DBP, the association is significant for both SBP and DBP but more marked for SBP than DBP, the effect is more pronounced the older the patient and NaCl dose strongly predicts SBP in older patients.