Evidence that the in vivo effect of papaya latex on H. bakeri is mediated through cysteine proteinases. Groups of mice infected with 200 L3 of H. bakeri were treated with water, E-64 alone, papaya latex (135 nmoles active enzyme) or papaya latex pre-incubated with E-64 (0.64 nM) for 15 minutes prior to oral delivery to mice. Only untreated papaya latex caused a significant reduction in worm burdens. For full analysis and further details, see Stepek et al . Reprinted with permission.