The relationship between severity score3 and pretreatment chitotriosidase activity of 15 Gaucher disease patients seen at the Shaare Zedek Gaucher Clinic. All patients in whom plasma chitotriosidase levels before treatment and chitotriosidase genotypes were available are included except for a patient with the homozygous null mutation. The activity of 2 heterozygotes was multiplied by 2, as is the usual practice. While a correlation is found, it is so weak that we would not want to base a $300 000-a-year treatment decision on this relationship.