The uptake of organic anion, p-aminohippurate (PAH), and organic cation, tetraethylammonium (TEA), was measured in cortical slices and plasma membrane vesicles isolated from the proximal tubule of ischemic rabbit kidneys. The uptake of PAH or TEA in cortical slices increased after 30 or 60 min of ischemia. When the kidneys were reperfused for 30 min, the uptake of organic ions returned to control levels. When ischemic (60 min) slices were preincubated for 120 min in an oxygenated medium, the stimulatory effect of ischemia on organic ion uptake was not observed. The PAH uptake by basolateral membrane vesicles and brush border membrane vesicles (BBMV) was not altered following 60 min of ischemia. However, the TEA uptake by BBMV but not basolateral membrane vesicles was significantly reduced. The dissipation rate of H+ gradient across the BBMV was similar in control and ischemic kidneys. The Vmax for TEA transport in BBMV isolated from ischemic kidneys was significantly reduced, but the Km was not altered. These results indicate that the organic cation secretory system is more vulnerable to ischemia than the organic anion secretory system in the rabbit renal proximal tubule.