Preliminary mammalian safety tests were conducted on the entomopathogenic fungusMetarhizium anosipliae. No animals died or were clinically ill after injection of or exposure toM. anosipliae. There was no evidence of ocular irritation, and tissue lesions were confined to local sites at which large numbers of spores were collected. There was no histologic evidence of spore germination in mammalian tissues.M. anosipliaewas recovered from stomach, lung, and spleen after 2 weeks of exposure of mice to dusts but not at the end of week 3. Fungi were recovered also from focal granulomas that followed intraperitoneal injections ofM. anosipliaespores into rats. Fungi were recovered from spleens of rats given spores intraperitoneally, but the spleens were sterile 21 days after exposure.We concluded that our tests reveal no evidence of human or mammalian pathogenicity ofM. anosipliae.