Gaucher disease is caused by a deficiency of glucocerebrosidase. It is the first lysosomal storage disorder for which effective enzyme-supplementation therapy has become available. The enzyme, alglucerase, is glucocerebrosidase derived from human placental tissue; its oligosaccharide chain has been modified to expose terminal mannose residues, facilitating uptake in macrophages. Many patients have been shown to benefit from treatment with the enzyme. Spleen and liver volumes decrease and cytopenia improves. Over a longer period of time, bone involvement can also be diminished, although severe pre-existing bone abnormalities do not change. The safety profile of alglucerase seems excellent, with only few adverse events and approximately 12% of patients developing antibodies. Because long term safety is unknown and the enzyme is very expensive, studies have focused on the determination of the optimum individual dosage. Different dosages have shown to be effective, but so far the identification of patients who need a high or a low dosage is unclear. Other issues that deserve attention are the selection criteria for the initiation of treatment and the place of prophylactic treatment. Diversity in the course of the disease, which in many cases cannot be predicted by genotyping, hampers the establishment of strict rules. Multicentre studies, in which comparison of data is made possible by the use of standardised measurements of disease manifestations, may be needed to solve these issues.