The multiplication of Mycobacterium leprae was modified by graded dilutions of organic acids. 0.01%-0.05% gluconic acid inhibited its multiplication. 0.005% of it promoted the growth of 2 out of 6 strains. 0.2% - 1.0% glucuronic acid promoted the multiplication of the majority of strains. 2.0% inhibited their multiplication, and 0.05% promoted the growth of one strain. Galacturonic and pyruvic acids were active in 0.2 - 2.0% concentrations, while the activity of citric acid was mainly noted at 1.0 and 2.0% concentrations.