It has been suggested that dietary linoleic and gamma-linolenic acid may be hypotensive. Fat enriched diets increase blood pressure, and the effects of linoleic and linolenic acids on this increase have been investigated. After a control period on a low fat diet, rabbits were given four fat enriched diets containing different proportions of linoleic, gamma-linolenic and alpha-linolenic acids for 8 weeks, and returned to the low fat control diet for 3 weeks. Blood pressures were measured non-invasively every day. Blood pressures increased from the 4th week of fat feeding. The blood pressure increase at 8 weeks was 10%, 13%, 15% and 14% respectively for primrose, starflower, safflower and olive oils (all P less than 0.001). Return to the low fat control diet for 3 weeks restored blood pressures to near control values. These results do not support the suggestion that either linoleic or gamma-linolenic acids are effective antihypertensive agents.