We studied the changes of potassium and sodium contents in erythrocytes and the activity of erythrocyte membrane Na(+)-K(+)-ATPase in 40 cardiac blood samples of rabbit corpses at different postmortem intervals (PMI). The erythrocyte potassium content (RBCK) decreased linearly as the PMI increased (R = -0.829, P < 0.025). during postmortem 48 hours. The erythrocyte potassium content and the time after death had significant correlation. The activity of erythrocyte membrane Na(+)-K(+)-ATPase had no significant changes over postmortem 48 hours.