For >50 yr, N,N-diethyl-3-methylbenzamide (deet) has been the standard for arthropod repellents and has been an important tool to protect people from disease agents carried by ticks, mosquitoes, and other arthropods. However, some people avoid using deet because of concerns about adverse health effects. In 2007, a new repellent, BioUD, with the active ingredient 7.75% 2-undecanone, originally derived from wild tomato (Lycopersicon hirsutum Dunal f. glabratum C. H. Müll) plants, was registered by the U.S. Environmental Protection Agency. In the current study, repellent efficacy of BioUD was compared using arm-in-cage studies with 7 and 15% deet against the mosquitoes Aedes aegypti (L.) and Aedes albopictus Skuse. No differences were found in mean repellency over 6 h after application between BioUD versus 7 and 15% deet for Ae albopictus. For Ae. aegypti, no differences were found over the same time period for 7% deet. Compared with 15% deet, BioUD mean repellency was lower over the 6-h test period. Human subject field trials were conducted in North Carolina, United States, and Ontario, Canada, comparing the repellency of BioUD to products containing 25 and 30% deet. BioUD provided the same repellency or was more efficacious than 25 and 30% deet, respectively, in these studies. Laboratory trials were conducted to determine the repellent activity of BioUD against the American dog tick, Dermacentor variabilis (Say), on human skin and cloth. BioUD repelled ticks at least 2.5 h after application to human skin. On cloth, no differences in mean repellency were found through 8 d after application between BioUD and 7% deet. In a two-choice test for BioUD versus 15% deet on filter paper, ticks spent significantly more time on the deet-treated surface than the BioUD-treated surface. Based on these studies in toto, BioUD is an efficacious alternative to deet in its repellent activity.