Advances in the immunological identification of primitive haematopoietic cells have led to the development of various techniques for their characterisation and purification. The expression of the CD34 antigen by the stem cell compartment has been exploited for these purposes. Separation systems capable of isolating CD34+ cells on a large scale are finding use in the clinic. Areas of interest overlap for both researchers and clinicians, and efforts to mobilise, characterise, purify and transplant these cells continue. Different CD34 purification systems are reviewed, focusing on their possible applications in different research fields. Clinical results of CD34+ selection and the possible future applications of this technology in the clinic are also reported.