Genes encoding l-arabinose transporters in Kluyveromyces marxianus and Pichia guilliermondii were identified by functional complementation of Saccharomyces cerevisiae whose growth on l-arabinose was dependent on a functioning l-arabinose transporter, or by screening a differential display library, respectively. These transporters also transport d-xylose and were designated KmAXT1 (arabinose-xylose transporter) and PgAXT1, respectively. Transport assays using l-arabinose showed that KmAxt1p has Km 263mm and Vmax 57nm/mg/min, and PgAxt1p has Km 0.13mm and Vmax 18nm/mg/min. Glucose, galactose and xylose significantly inhibit l-arabinose transport by both transporters. Transport assays using d-xylose showed that KmAxt1p has Km 27mm and Vmax 3.8nm/mg/min, and PgAxt1p has Km 65mm and Vmax 8.7nm/mg/min. Neither transporter is capable of recovering growth on glucose or galactose in a S. cerevisiae strain deleted for hexose and galactose transporters. Transport kinetics of S. cerevisiae Gal2p showed Km 371mm and Vmax 341nm/mg/min for l-arabinose, and Km 25mm and Vmax 76nm/mg/min for galactose. Due to the ability of Gal2p and these two newly characterized transporters to transport both l-arabinose and d-xylose, one scenario for the complete usage of biomass-derived pentose sugars would require only the low-affinity, high-throughput transporter Gal2p and one additional high-affinity general pentose transporter, rather than dedicated d-xylose or l-arabinose transporters. Additionally, alignment of these transporters with other characterized pentose transporters provides potential targets for substrate recognition engineering.