January 1st 2003Champlin and colleagues haveelegantly summarized the conceptof nonmyeloablativestem cell transplantation (NST),stressing the importance of this newlyemerging procedure for the treatmentof patients with life-threateningmalignant hematologic and nonhematologicdiseases. This review doesnot include a description of the safetyand efficacy of NST for the treatmentof many life-threateningnonmalignant diseases for which noalternative therapy exists. This categoryencompasses a long list of geneticdisorders, diseases caused by adeficiency of stem cell products, andsyndromes associated with immunedeficiency. However, discussion ofthese illnesses is beyond the scopeof this review, which focuses oncancer.