Abstract.The content of microaggregates was determined in leukocyte‐poor red blood cells (RBC) after 5 weeks of storage in citrate‐phosphate‐dextrose (CPD)‐adenine plasma and in saline‐adenine‐glucose‐mannitol (SAGM) medium. The size range was 3,600‐200,000 fl, corresponding to a particle diameter of 19–73 μm, presuming a spherical particle shape. In comparison with CPD‐adenine whole blood (100%), the total number of particles per unit of RBC was found to be 41.2% (CPD‐adenine anticoagulant) and 25.4% (SAGM medium). The corresponding data for total particle volumes were 43.3 and 30.3%. The significant differences between the two categories of RBC could not be explained on the basis of differences concerning pH or cell composition. A majority of particles (50–62%) was observed in the lowest size range (19–29 μm), corresponding to only 18–26% of the total particle volume. The accumulation of di‐2‐ethylhexylphthalate (DEHP) was determined in two variations of RBC stored in SAGM medium and in RBC stored in CPD‐adenine plasma. The quantities of DEHP per unit of RBC after 5 weeks were significantly smaller in SAGM medium (9.0 ±3.6 and 22.7 ± 6.1 mg, respectively) compar