Lysosomal storage disorders (LSD) arise from genetic deficiency of a lysosomal enzyme (or its transport) and from subsequent accumulation of the enzyme substrates. Haemopoietic Stem Cell Transplant (HSCT) therapy for LSD corrects disease through cross correction of enzyme deficiency in recipient cells by enzyme secreted from engrafted, donor blood cells. The process of such transplant, its efficacy and its inherent risks are central in defining its current place in therapy. Two decades of HSCT have seen dramatically improving results as well as an improved understanding of the factors that affect outcome in both the short and long term. With improving survival figures transplant might become a viable treatment for patients that were traditionally excluded from transplant because of perceived risk. Some LSD respond better to HSCT than others and even within a responding disease some organs respond better than others. We develop the concept of delivered enzyme following cellular and other therapies of LSDs, including pharmacological enzyme replacement therapy (ERT). Delivered enzyme must be sufficient to achieve a correctable threshold that is both tissue and disease specific. Therapies of LSDs in the future will be more effective as they improve enzyme delivery to tissues and do so more safely and with reduced long term toxicities.