This first part of the review deals with fundamental knowledge, rationale and methods for the use of autologous bone marrow transplantation in the treatment of neoplastic diseases. Use of high-dose chemo- and radiotherapy in the treatment of neoplastic diseases is limited by side effects on haemopoietic tissues. Bone marrow transplantation offers a possibility to escalate the dose of cytotoxic therapy, but this possibility is limited by two main factors: need for matched allogeneic donor, and patient age below 45 years. This has led to application of autologous BMT for the treatment of older patients and those without compatible marrow donors. Samples of bone marrow collected before intensive myeloablative treatment are stored by means of cryopreservation. Viability and clonogenicity of stored bone marrow stem cells prior to reinfusion into the patient are tested by in vitro bone marrow culture (usually CFU-GM). Treatment of marrow samples in vitro by monoclonal antibodies and/or cytotoxic drugs are used in order to cleane ("purge") the marrow of residual neoplastic cells.