Rodent feed is sterilized to eliminate the introduction of potentially pathogenic microorganisms that might result in clinical disease or subclinical infections that could affect physiologic responses. This practice became common as the demand for SPF animals increased. On rare occasions, we have isolated enteric pathogens, including Salmonella spp., Escherichia coli, and Clostridium spp., from unsterilized, natural ingredient rodent feeds (unpublished data). Recent publications regarding the isolation of contemporary, relevant rodent pathogens from rodent diets are unavailable; however, several recent reports implicated the persistence of mouse parvovirus in mouse colonies due to the use of unsterilized feed. 31,40 Current feed sterilization methods are steam autoclaving and irradiation. The chosen method may depend on an institution's capabilities or budget. Steam autoclaves require a large initial capital investment, ongoing maintenance, and a lot of energy to operate. In contrast, few institutions have the capabilities to irradiate feed on a large scale, so most irradiation of feed is performed by or through the feed manufacturers and can add a substantial cost to the feed. Neither method will sterilize all loads 100% of the time. Sterilization depends on load size and ability for adequate quality steam or radiation penetration. Both methods of sterilization can affect the quality of the feed. Many groups, including ours, have shown that autoclaving rodent feed increases feed pellet hardness. 16,35 Feed pellet hardness can affect rodents' ability to eat, especially young animals or strains with dental issues. 23,24 Autoclaving rodent feed can result in decreases in vitamins A, B1, and D; affect protein quality and availability; and alter isoflavone content. 9,15,36 To compensate for the vitamin loss, feed manufacturers often add additional vitamins to the feed mix for autoclavable formulations. Irradiation has little effect on the physical quality of feed but can alter its chemical composition. Feeding an irradiated, purified, AIN76 diet to germ-free mice resulted in high mortality (50%) that was ameliorated with vitamin K supplementation. 20 SPF cats fed an irradiated diet developed a progressive hindlimb ataxia suspected to be due to vitamin A deficiency. 7,13 More recently, irradiation has been shown to increase glycosinolates and the peroxidation of dietary lipids. 8,30 In 2002, studies found that heating foods containing high levels of starches resulted in the production of acrylamide (C 3 H 5 NO; prop-2-enamide) 34 through the Maillard reaction between amino acids (primarily asparagine) and reducing sugars. 26,33,41 Soon after, acrylamide production was demonstrated in autoclaved rodent feed. 37 Acrylamide is a compound used widely in the chemical industry for numerous purposes (paper, grouting agents, water treatment, and cosmetics) and occurs in cigarette smoke. Acrylamide is a neurotoxin, 25 genotoxin, 4,10,12,17