Since Rooibos tea contains high levels of flavonoid antioxidants with potential health benefits when taken orally or applied topically, the quantity of the antioxidants crossing the physiological barriers is of scientific, clinical and commercial importance. This study investigated the in vitro transport of aspalathin, a unique flavonoid constituent of Rooibos tea, across intestinal epithelial cells and the human skin. The transport studies were conducted for both pure aspalathin solutions and extracts from unfermented (or green) Rooibos (Aspalathus linearis) aerial plant material across human abdominal skin in vertical Franz diffusion cells and Caco-2 cell monolayers in Transwell 6-well plates. The results obtained from the percutaneous permeation studies demonstrated that only 0.01% of the initial aspalathin dose from both the test solution and extract permeated through the skin, which was in accordance with the prediction from its log P value of -0.347. A portion of 0.07% of the initial aspalathin dose penetrated the different layers of the skin for the green Rooibos extract solution and 0.08% for the pure aspalathin solution. The transport of aspalathin across Caco-2 cell monolayers was concentration dependent and reached almost 100% (P(app) = 20.93 x 10(-6) cm/s) of the initial dose in the highest concentration tested for the extract, while it was only 79.03% (P(app) = 15.34 x 10(-6) cm/s) of the initial dose for the highest concentration of the aspalathin solution.