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Chemical repellents derived from predators might offer more effective and longer lasting protection from vertebrate depredations than current damage control measures. Thus, we conducted laboratory and field studies to evaluate the repellency of mongoose feces and urine to black rats (Rattus rattus) and Polynesian rats (R. exulans ) . We exposed captive wild rats to water, butyric acid, mongoose (Herpestes auropunctatus) feces, or mongoose urine in a 150- x 60- x 120-cm partitioned arena and recorded their behavior with a video camera. None of the test substances had any apparent effect (P> 0.05) on behavior or the percentage of observations spent (1) in the transfer cage, (2) in tunnels, (3) on the side of the arena with the treatment, (4) in, on, or near the tunnel with the treatment, or (5) in the tunnel with the treatment. Nor did we observe any effect on latency until rats emerged from the transfer cage or entered the treated tunnel or time spent in the treated tunnel during their first visit. During the field test, we set and monitored 50 pairs of live traps along each of 12 transects in forested areas and along the perimeter of recently harvested sugarcane fields. Mongoose feces or urine was applied to one trap in each pair. We captured 49.2 rats (R. rattus and R. exulans) per transect during 4 nights of trapping. We captured fewer (P< 0.05) rats in traps soiled with mongoose feces than traps soiled with mongoose urine or unsoiled traps. The gender of the mongoose that was the source of the feces or urine had no effect (P>0.05) on capture success. The discrepancy between the laboratory and field studies indicates that researchers should incorporate relevant factors in the natural environment into their test paradigm and interpret the results of tests with captive animals cautiously. Additional research is warranted to determine the active compound(s) in mongoose feces that repel rats and to explore the use of such compounds to reduce rat damage to agricultural crops.