1. A cerebral perfusion method was used to measure the net uptake of arabinose from the circulatory system in cats.2. There was found to be discrimination between the optical isomers of this substance, with apparently greater uptake of the (-)-form.3. The uptake process was highly temperature dependent, with a Q(10) of 3.0.4. The uptake of arabinose was partially inhibited by 1 mM ouabain perfused concurrently. It was not significantly inhibited by dinitrophenol or phlorrhizin.5. Glucose inhibited competitively the uptake of (-)-arabinose.6. We conclude that the mechanism involved is of the carrier-mediated or of the active transport type, and that at least part of it is shared with glucose and probably other sugars.