The effects of select drugs, dosages, and modes of administration upon learned taste aversions were compared among groups of wild-caught male and female Philippine rice rats (R. r.mindanensisi. Experiment 1 compared two-choice saccharin aversions for 28 days among groups intubated with copper sulfate, cyclophosphamide, lithium chloride, red squill, sodium chloride (control), or deionized water (control). Main results were that 375 mglkg lithium chloride produced the greatest sustained aversions, whereas 198 mg/kg cyclophosphamide and 210 mglkg red squill produced moderate aversions, with males showing more resistance to extinction than females. Experiment 2 compared saccharin aversion among matched groups of male and female rats that received low (36 mg/kg], moderate (105 mg/kg), or high (368 mglkg) dosages of lithium by gavage, ip injection, or ingestion. Sex differences in rates of extinction were found for the ingestion and injection-dosed rats, but no sex difference was again found for rats dosed by gavage. A significant mode X day interaction indicated that extinction progressed more rapidly for rats dosed by gavage. For all modes of administration, high dosages yielded intense 28·day aversion, moderate dosages produced intermediate 3·5 day aversion, and low dosages caused no aversion.