Epidemiological studies and clinical trials have consistently shown an inverse association between potassium intake and blood pressure. As a means of raising potassium intake within the UK population, an increase in the consumption of fruits and vegetables is strongly advocated. The aim of this study was to determine the bioaccessibility of potassium in these foods. A 10-day crossover feeding trial was performed on 11 healthy volunteers. For 5 days a diet providing most of the potassium in the form of unprocessed fruits and vegetables was followed by a diet in which the potassium was believed to be almost wholly bioaccessible, being derived from animal foods and fruit juices. The potassium and sodium of the diets and the urine were determined by chemical analysis: 96.3% of the potassium in the 'high bioaccessible diet' was recovered in the urine, compared with 76.8% from the diet rich in fruits and vegetables. This difference is attributed to the cellular structure of plant foods. The relatively poor bioaccessibility of potassium diminishes the perceived nutritive value of these foods with regard to potassium intake.