Two experimental controlled-release repellent formulations containing 35% (3M) and 44% (Biotek) deet, respectively, were compared with a 75% standard formulation of deet used by the military. The military repellent was equal to or significantly better than the formulations in duration of protection against 2 mosquito species in laboratory and field tests, but the formulations contained only 47-59% the amount of deet in the military repellent. In all cases high levels of protection (greater than 95%) were measured, but because of high densities of biting mosquitoes in field tests, this level did not necessarily indicate few bites. In terms of mean bites/test/day by Anopheles quadrimaculatus in caged tests, the military repellent had fewest (2) and Biotek had most (41).