AbstractRed cells stored under blood bank conditions normally show less than 1% spontaneous in vitro hemolysis even after 5 weeks; larger hemolysis may be found if the cells are suspended and stored in a saline‐adenine‐glucose (SAG) solution with very little trapped plasma. Delay of the addition of the suspension medium, return of 25 ml plasma after a maximal plasma harvest, addition of mannitol 10–30 mmol.1‐1to the suspension medium were alternative and effective ways of keeping the spontaneous lysis within normal limits. Mechanical traumatization (centrifugation or shaking) caused considerably more damage to the red cells when these were highly concentrated than when they were diluted. A cell suspension in SAG is a more suitable product for hemotherapy than strongly packed red cell conce