The objective of this study was to test the effect of a supplement of blackcurrant seed oil (BSO), a rich source of gamma-linolenic acid (C18:3n-6) on the resting blood pressure (BP) and cardiovascular reactivity to a psychological stress in borderline hypertensive individuals. Twenty-seven male volunteers found to have a BP lying persistently within the borderline range, were allocated randomly to one of two groups at the end of a 4-week baseline period. The first group received a daily supplement of 6 g safflower oil for the consecutive 8 weeks while the second the same dose of blackcurrant seed oil. In addition to weekly measurements of resting BP, BP and heart rate reactivity to a standardised 5-min test of mental arithmetic were recorded before, and at the end of the supplementation period. BSO inhibited BP reactivity by over 40% (ANOVA for repeated measures diastolic (D) BP P = 0.026, systolic (S) BP P = 0.021). The decrease in DBP for the subjects on BSO was significantly different from the slight changes observed in the safflower group (ANOVA for repeated measures P = 0.018 for time-treatment interaction). We conclude that gamma-linolenic-rich fatty acid preparations are likely to influence cardiovascular control, by mechanisms yet to be clarified.