The effect of the lipopolysaccharide preparation (PMKO) on the development of macroscopic lesions in the corneas of mice challenged intracorneally with Mycobacterium tuberculosis was studied. When saline suspensions of PMKO were used, there was no effect on the development of lesions in the cornea. When liquid paraffin suspensions of the lipopolysaccharide were used, there was a small reduction in the size of the macroscopic lesion obtained in the cornea. With 2 doses of 50 y (given at an interval of 14 days) the effect was significant. On a weignt-for-weight basis, phenol-killed M. tuberculosis is more immunogenic than the lipopolysaccharide.