1. Theoretic effectiveness of different types of exchange transfusions has been determined.
2. Homogeneous and nonhomogeneous solutions used as the exchanging medium differ in final results obtained.
3. The final concentration of original eryrthrocytes (in per cent of total red cells in the circulation) diminishes as the ratio of donor to patient’s initial hematocrit increases for the same volume exchange.
4. Final hematocrit values may be obtained from the calculated data.
5. Optimum considerations for exchange transfusions are discussed.