1. The effects on blood pressure of dietary fish oil, sodium restriction and a combination of both strategies were examined in a short-term dietary intervention study of 50 healthy elderly subjects (average age 67 years) with mean initial systolic and diastolic blood pressures of 133 and 77 mmHg, respectively. 2. Subjects were allocated to one of four treatment groups: fish oil with normal sodium, fish oil with low sodium, sunflower oil with normal sodium and sunflower oil with low sodium for 4 weeks. They then crossed over to the alternative sodium treatment for a further 4 weeks whilst remaining on the same oil. 3. The combination of fish oil supplementation with dietary sodium restriction caused significant reductions of blood pressure in the first 4 weeks: systolic blood pressure (SBP) fell by 8.9 mmHg, mean arterial pressure (MAP) by 7.4 mmHg and diastolic blood pressure (DBP) by 6.0 mmHg. 4. Fish oil enhanced the effect of sodium restriction on blood pressure. In the crossover protocol, a change in sodium excretion of 92 mmol/day was accompanied by changes of 6.4, 3.3 and 2.2 mmHg for SBP, MAP and DBP, respectively, in the subjects taking fish oil. However in those taking sunflower oil, blood pressure did not change significantly. 5. The results indicate beneficial interactive effect of dietary fish oil and sodium intake on blood pressure.