Bees were tested by exposing them in cages under controlled conditions to the action of different chemicals through contact, fumigative and stomach poisoning effects. The measure of toxicity was regulated by the amount of material necessary to cause death to a median number of bees within 3 days time in order to reduce the probable error of natural death rate. Observations made in the field were taken as a check on results in the laboratory. The materials tested were benzene hexachloride (90% gamma isomer), chlordan, dichlorodiphenyl dichlorothane, DDT, hexaethyl tetraphosphate, parathion, tetraethyl pyrophosphate, toxaphene and an exptl. compound (J.H. 118) closely related to chlordan. None of the chemicals were sufficiently repellent to bees to prevent their injury. The L.D.50 in 72 hours in microg. per bee for the different chemicals was given as follows: toxaphene 22.0, dichlorodiphenyl dichlorothane 16.0, DDT 4.6 (at room temp.) and 12.0 + at 95[degree]F, chlordan 1.21, tetraethyl pyrophosphate 0.75, hexaethyl tetraphosphate 0.29, "J. H. 118" 0.25, benzene hexachloride 0.15, and parathion 0.07. All chemicals but dichlorodiphenyl dichlorothane exhibited significant contact toxicity and benzene hexachloride, chlordan, "J. H. 118" and parathion indicated considerable fumigant toxicity.