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In some situations chemical repellents are a socially appealing nonlethal alternative to reduce deer (Odocoileus spp.) damage to plants. New products are continually becoming available, but their ability to repel deer is very variable. We tested 20 repellents representing 4 modes of action (fear, pain, taste, and aversive conditioning) and 2 delivery systems (topical applications and area repellents [scent packets]) to evaluate current products and identify trends that could be used to predict efficacy of future products. During fall 1998, we placed treated western red cedar (Thuja plicata) seedlings in pastures with black-tai led deer (Odocoileus hemionus) and recorded number of bites taken from each seedling at weekly intervals for 18 weeks. Four of the 5 most effective repellents used fear as a mode of action. We tested the 5 most effective repellents again in spring 1999 when trees were growing actively and were more palatable to deer. Only PlantskyddTM and Deer Away Big Game Repellent@ powder reduced damage. However, unlike the winter study, the Deerbuster'sTMand Bye Deer® sachets were hung on stakes at half the height of the seedlings instead of near the terminal buds. When an additional study was conducted with the sachets mounted near the terminal buds so that repellent could drip from bags onto the plants as in the winter study, Deerbuster's sachets and Bye Deer sachets reduced deer foraging. In general, products using fear as a mode of action were more effective than products using other modes of action and topical repellents were more effective than area repellents.