Abstract: Repellent compositions which contain aromatic aldehydes such as cinnamic aldehyde, .alpha.-hexyl cinnamic aldehyde and/or coniferyl aldehyde are provided, together with methods for their use as repellents for pests including flies, cockroaches, aphids, silverleaf white flies, mosquitoes, ticks, fleas, lice, leafhoppers, thrips, two-spotted spider mites, snails, slugs, biting midges, earwigs, and moths. Also provided are stabilized .alpha.-hexylcinnamic aldehyde (HCA) compositions which reduce the evaporation rate of HCA and/or induce HCA to evaporate at a constant rate over time.