There seems to be a greater variation between laboratories in hydrogen peroxide hemolysis techniques than in other clinical laboratory procedures. In this report, factors influencing hemolytic values were examined and the effect of the combination of these factors on the results was analysed statistically by using the orthogonal array. Factors influencing hemolysis induced by hydrogen peroxide were as follows; the concentration of hydrogen peroxide, temperature in the peroxide reagent when added to the red cell suspension, the red cell concentration in the cell suspension and the addition of charcoal to the reaction mixture. However, addition of charcoal may not be essential to stabilize the hemolytic values and other factors such as keeping blood for 4 hours at room temperature before testing, the difference between investigators, a reaction time 2 or 3 hours and the technique of adding peroxide reagent to the cell suspension, had little effect on hemolysis. The most important factor was the temperature in hydrogen peroxide solution. The estimated hemolytic values by the orthogonal array linearly correlated with the plasma tocopherol levels.