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Sucrose aversions were induced by lithium chloride toxicosis in 9-week-old male and female mice of the C57BL/6J and DBA/2J strains. Under conditions of ad-lib access to fluids which required a long interval between the sucrose and toxicosis, the conditioned aversions were relatively weak when compared with the sucrose consumption of saline-injected controls. The aversions extinguished rapidly within all groups. Contrary to earlier reports in rats, no sexual dimorphism in extinction rate was observed in this paradigm. When a fluid·deprivation schedule was implemented in the conditioning procedure to shorten the interval between taste experience and toxicosis, strong aversions were noted; yet relatively fast extinction under ad-lib conditions occurred in all groups except male DBA/2J mice. No sexual dimorphism was observed in mice of the C57BL/6J genotype, even when two pairings between sucrose and toxicosis were administered.Chambers and Sengstake (1976) reported sexual dimorphism in the rate at which rats extinguish aversions to sucrose solutions induced by lithium chloride (LiCI) toxicosis. Using this conditioned taste aversion (CTA) paradigm, systematic research by Chambers (1976) providedevidence of the involvementof testosterone in this learning phenomenon. Specifically, mature male rats exhibit much stronger resistance to extinction relative to that reported for mature female rats, but the extinction pattern of castrated male rats parallels that of female counterparts, both intact and castrated. When castrated males and females are provided testosterone propionate replacement, the course of CTA extinction is similar to that of intact males. Replication of this work investigated possible estrogenic and androgenic components of the testosterone effect (Earley & Leonard, 1978). Androgens, but not estrogens, were found to mediate the slower rate of CTA extinction observed in male rats.Further investigation demonstrated that the phe-