O-phenyl phenol (OPP) was evaluated in tests designed to simulate its proposed use as a fumigant by archives and libraries to control fungus growth. It was compared with thymol (isopropyl-meta-cresol) for its ability to render the spores of seven species of common fungi non-viable, and it was found that although each fumigant had the ability to stop or retard fungus growth, neither was totally effective in preventing fungus spores from germinating.