Five closely related organic thiocyanates were synthesized and their insecticidal properties compared with that of γ -thiocyanoproyl phenyl ether, previously tested. Of these compounds one, namely, trimethylene dithiocyanate, was definitely superior to the above mentioned ether, while the remainder were distinctly inferior. Trimethylene dithiocyanate was considerably more toxic than its isomer, propylene dithiocyanate. Trimethylene dithiocyanate gave satisfactory control in laboratory tests on APhis rumicis, the melon aphid (Aphis gossypii), the citrus mealy bug (pseudococcus citri), the long-tailed mealy bug (Pseudococcus adonidum), the lesser European bark beetle (Scolytus multistriatus), the potato flea beetle (Epitrix cucumeris), and the red spider mite (Tetranychus telarius). Of 75 species and varieties of plants tested with regard to their tolerance to trimethylene dithiocyanate (0.1 per cent) 64 were tolerant as compared with 59 for γ -thiocyanopropyl phenyl ether used at the same concentration.