Purified tubercle bacillus was dissolved in n-hexadecane and suspended in water was a good immunizing agent against experimental tuberculosis in mice. It was effective by either subcutaneous or intraperitoneal injection. The purified tubercle bacillus wax contains many solvent-extracted tubercle bacilli. The wax lost its immunizing power when these bacilli were removed by ultracentrifugation. The wax is a stable antigen and retained considerable antigenicity after autoclaving.