By convention, peripheral blood stem cell products for autologous transplantation are evaluated for quality by CD34 + cell dose at the time of harvesting. A CD34 + cell dose in excess of 2.0×10 6 /kg of recipient body weight is considered adequate for haematopoietic engraftment. Viable CD34 + cell numbers are enumerated in most laboratories using the ISHAGE single platform flow cytometric method which utilizes monoclonal antibodies to CD45, CD34 and 7 amino actinomycin D (7AAD) dye exclusion.One hundred and six consecutive autologous transplantation procedures underwent viable CD34 + cell enumeration at the time of harvesting and post thaw prior to re-infusion. Neutrophil and platelet engraftment and markers of haematopoietic support were analyzed.Mean pre-cryopreservation viable CD34 + numbers were 4.882×10 6 /kg. Mean post thaw viable CD34 + numbers were 3.234×10 6 /kg. Mean loss of viable CD34 + cells with processing and cryo-preservation was 1.648×10 6 /kg (33%). For neutrophil engraftment, there was no significant difference between high (⩾3.0×10 6 /kg) and low (<1.5×10 6 /kg) post thaw viable CD34 + cell counts (p=0.545). For platelet engraftment, there was however a significant difference observed between the high and low pre infusion viable CD34 + groups (p<0.001). Additionally, significant differences were seen between the post thaw viable CD34 + cell count and the associated length of hospital admission, days of use of G-CSF post transplantation, use of antibiotics in the post transplantation period and transfusion support in the post transplantation period.A significant loss of viable CD34 + cells occurs during processing, cryopreservation and thawing. Low numbers of viable CD34 + cells infused post thaw will still result in adequate neutrophil engraftment however may delay platelet engraftment. Low viable CD34 + cell numbers have significant effects on admission duration and use of haematopoietic supportive measures with consequent effects on healthcare resources.