ABSTRACT Novel aromatic and aliphatic organic acids, esters and ketones were synthesized and assayed as repellents for ticks. E-7-(cyclohexyl)hept-4-enoic acid (CHEA), E-7-phenylhept-4-enoic acid (PHEA), ethyl E-7-(cyclohexyl)hept-4-enoate (CHEN) and ethyl E-7-phenylhept-4-enoate (PHEN) had repellent activity against the soft tick, Ornithodoros parkeri (Acari: Argasidae) in a two-choice filter paper bioassay. PHEN, an aromatic organic ester, was the most active. 2-undecanone, a natural product found in the trichomes of wild tomatoes, was found to mimic our lead chemistry and was active as a repellent at 50 μg/cm2. Since this compound is an already known natural botanical with a proven safety record including being approved as a food additive, formulation studies were conducted to optimize its volatility and maximize its repellent activity against ticks and insects when applied to human skin. Using proprietary technology from HOMS LLC, we were able to develop BioUD. BioUD30 and BioUD8 was a repellent to the American dog tick, Dermacentor variabilis, 2.5 h after applications on the skin of human subjects. BioUD8 was also active after 2.5h against Ixodes scapularis. BioUD8 at 6 h after application was better than OFF Botanicals with 10% PMD and equivalent to OFF with 15% DEET against mosquitoes under practical field conditions. Application of 20 μl BioUD30 (30% undecanone; 5.88mg) to ~9.8 cm2 of cotton fabric repelled on average >90% of D. variabilis ticks in a two-choice bioassay, 5 d after application, suggesting that it binds to cotton fabric. BioUD will be marketed by HOMS LLC as a DEET replacement. BioUD will be all natural and non-flammable unlike many DEET products, with the potential of being organically certified. The US EPA registration was submitted in March 2006 with a six months evaluation schedule.