Lysozyme is an enzyme that inhibits a broad spectrum of gram-positive bacteria and some fungi. It may have potential as an alternative to conventional antibiotics to treat brood diseases of Apis mellifera and has the advantage of being a food-safe additive. After establishing the laboratory activity (MIC) of hen egg albumen lysozyme against honey bee pathogens, its toxicity to bees and in vitro activity against Paenibacillus larvae was evaluated. The acute and chronic oral toxicity of lysozyme to adult workers was determined using cages of nurse-aged bees, treated and incubated in the laboratory. Cages were administered doses from 0 - 6400 µg lysozyme/bee over 72 h. Lysozyme was virtually non-toxic to adult workers (24-h LD₅₀ >6400 µg) and was less toxic than oxytetracycline. Chronic consumption of lysozyme caused reductions in longevity between 2-12 days, depending on dose. Effects on larvae were evaluated using an in vitro rearing assay. Larvae were fed doses ranging from 0-10% lysozyme and, when infected, had 1.5 x 10⁸ P. larvae spores/mL mixed in their basic larval diet (BLD). Although lysozyme was not toxic to worker larvae at doses ≤4% in BLD, it killed all the larvae during the pre-defecation stage when fed at 10% in BLD. Toxicity of doses > 4% was significantly greater than that of 0.0025%, which was the only dose that reduced mortality to P. larvae. This wide range between toxic and therapeutic doses provides some promise for disease control. Suppression of Ascosphaera apis infections will also be discussed.