Natural products consisting of amides, lactams, lactones, ketones, monoterpenes, and sesqiterpenes have been identified and successfully explored as insect repellents. In our laboratory and at participating institutes we have been pursuing structure activity relationship (SAR) of numbers of such natural product extracts and isolated compounds for their insect repellency against biting arthropods. Simultaneously we have demonstrated that by simple chemical modifications of natural products, structurally related compounds exhibiting potent insecticidal and insect repellent activities can be enriched. Utility of available and modified in vitro screening methods to determine repellent efficacy of candidate compounds against biting arthropods will be discussed.