The relationship between the extracellular potassium concentration (K+ e.c.) and the resting membrane potential (MP) of the gastrocnemius muscle was studied in the anesthetized rabbit during a 3-h period of hindleg ischemia and a subsequent 1.5-h period of resumed flow. The K+ e.c. was measured on the skeletal muscle surface, using a potassium selective electrode. The MP was recorded with conventional microelectrodes. Small biopsies were taken and analysed for content of ATP and lactate. The lactate content increased fourfold during the ischemic period, but returned to normal values after reflow. No significant changes occurred in the ATP content during the period of the experiment. K+ e.c. increased from 3.6 +/- 0.2 to 16.1 +/- 0.7 mmol/l, and the MP decreased from -90.2 +/- 0.6 to -58.5 +/- 1.9 mV during the 3-h period of ischemia. After release of the tourniquet there was an initial rapid decrease in K+ e.c. to 7.8 +/- 0.9 mmol/l during the first 15 min of resumed flow, followed by a slower decrease. The MP increased linearly during the first hour of resumed flow and both variables returned to near normal values 1.5 h after releasing the tourniquet.