Objectives: This was a pilot study to determine (1) whether it is feasible to effectively blind human subjects to the presence of the insect repellents N,N-diethyl-m-toluamide (DEET) and permethrin; (2) whether DEET affects the absorption of permethrin; and (3) whether combat videotape viewing and mental arithmetic are stressful. Methods: Ten volunteers were exposed to DEET, permethrin, and stress (1-hour combat video-tape plus mental arithmetic) in a double-blind, randomized, placebo-controlled trial. Outcome measurements included hemodynamics, plasma DEET and permethrin levels, and questionnaires to assess blinding. Results: Highly sensitive serologic assays readily detected DEET but not permethrin. Staff members and subjects were effectively blinded to both. The videotape-math combination was stressful by both self-report and hemodynamic measures. Conclusions: It is possible to blind subjects with respect to DEET and permethrin. Permethrin on clothing does not enter the bloodstream at appreciable levels. Combat videotapes and mental arithmetic can be stressful.