AbstractIn 50 individuals, intensive harvesting of relatively pure mononuclear cell fractions from the peripheral circulation was carried out in 195 procedures. Serial collections from bone marrow donors (group 1: n = 35) or isolated procedures from volunteers (group 2: n = 15) were without morbidity. A median yield of 4.0 × 109mononuclear cells were recovered in a final volume of 104 ml of cell‐rich plasma, for which 4,300 ml of venous blood was processed in 107 minutes. In neither group were changes documented in donor white cell count or lymphocyte numbers. In group I, a statistically significant but clinically unimportant and transient fall occurred in the platelet count at the end of the 5‐day intensive schedule. It is concluded that mononuclear fractions can efficiently be collected from normal donors without the development of relevant cell deple