&NA;A new method of measuring intracellular Na and K using Li substitution analysis was applied to a study of red cell Na changes in hemorrhagic shock. Using a rat hemorrhagic shock model, significant changes in red cell Na were found after 2 hours. Red cell Na in shocked animals was significantly higher than in control animals (p< 0.025). A small decrease in red cell K occurred. There was no intracellular shift of Li. In addition, a fall in plasma Na and a rise in plasma K occurred with progressive shock. In a 2‐hour period following retransfusion there was no significant change in cell Na or K, but the plasma Na and K returned toward preshock levels. These results confirm a prolonged and significant impairment of red cell membrane function in shock and suggest that impaired Na‐K pump function may be responsible for the changes.