Certain dietary polyunsaturated fatty acids, gamma linolenic (18:3n-6) and eicosapentaenoic (20:5n-3) acid, attenuate cardiovascular reactivity to stress in rats. To study their effects on cardiovascular reactivity to acute stress in man, 30 men were randomly assigned to one of three groups and given 28 day supplements of borage oil (containing 18:3n-6), fish oil (containing 20:5n-3), or olive oil (placebo). Reactivity to the Stroop colour-word conflict test was assessed prior to and following treatment. Borage oil alone attenuated blood pressure and heart rate responses to stress, increased skin temperature, and improved task performance. These data suggest that diet may be used to alter stress reactivity in man.