To better protect military personnel from insect bites and from the health problems associated with insect bites, the Army would like an improved insect-repellent formulation using N,N-diethyl-m-tolulamide DEET as the active ingredient. The improved formulation should be efficacious for a longer period of time than repellent formulations that are presently available. And, the improved formulation should have properties that would encourage military personnel to use it. The objective of this research program was to develop a long-acting, arthropod, repellent formulation that was efficacious for 12 hours. Several approaches were examined to afford a formulation that released DEET at a controlled rate. These approaches involved encapsulation techniques and included a variety of microcapsule preparations and film-forming preparations. A formulation consisting of 53 DEET and 47 inert ingredients showed improved efficacy over the repellent the Army is presently using. This improved formulation contained encapsulated and free DEET. Efficacy results from human testing with mosquitos demonstrated that the improved repellent formulation is significantly more effective for a longer period of time than the repellent the Army presently uses 75 DEET in ethanol. In addition to the development and evaluation of the improved repellant formulation, a unique trim package was designed and constructed for the formulation. Important technical improvements were made to measure the in vitro rate of evaporation of conventional and controlled-release repellents.