In poisoning operations, sublethal consumption of the toxin, can produce bait aversion. This decreases the effect of the poisoning and may create problems due to the presence of uneaten toxin in the environment. The use of new bait additives may prevent aversion development. Here I report the effects of two bait additives, corticosterone and mifepristone, in altering bait aversion development in rats exposed to the widely used poison, monofluoroacetate (1080). Corticosterone is a glucocorticoid hormone, released in response to stress.