SummaryLaboratory tests were designed for preliminary evaluation of compounds as repellents and toxicants for the protection of persons from fleas and ticks. Materials were desired that would be effective when applied to the clothing, and would remain effective through several days of wear or even through repeated washings. Elimination of the less effective compounds was rapidly accomplished by screening tests with small patches of treated cloth. Materials that were effective in the screening tests were further tested by applications to sleeves, stockings, or socks, which were worn in the presence of an infestation of fleas or ticks. Their safety for practical use has not yet been determined.The toxicants most effective and durable against both fleas and ticks were 3,5-dinitro-o-cresol, dinitro-o-sec-butylphenol, 95-per cent gamma-benzene hexachloride, and Lethane A-70 (beta, beta'-dithiocyanodiethyl ether). Nicotine alkaloid gave an exceptionally short knock-down time against both species. Chlordan, p-tolyl benzyl ether, omega-piperidinodecylbenzene, the p-dimethyl-aminophenyl ester of thiocyanic acid, and n-capric acid were also especially effective against fleas, and 2,4-dinitrophenol, laurylcyclohexylamine, n-amylvalone, the p-dimethylaminophenyl ester of thiocyanic acid, and the lauryl ester of thiocyanic acid against ticks.The most effective repellents were the N-(mixed monamyl)- and N-(n-amyl)-imides of 1,2-dicarboxy-3,6-endomethylene-4-cyclohexene, the tributyl ester of phosphoric acid, 4-chloro-3,5-xylenol, N-n-butylacetanilide, diethyl ester of phthalic acid, o-n-hexyloxybenzyl alcohol, the monocaproic acid ester of 1,5-pentanediol, n-capric acid, and p-iso-pentoxybenzyl alcohol.