Abstract Insecticidal fumigation toxicity of natural and synthetic cyanohydrins was evaluated with four stored‐product pests: the lesser grain borer, Rhyzopertha dominica (F), the red flour beetle, Tribolium castaneum Herbst, the saw‐toothed grain beetle Oryzaephilus surinamensis L, the maize weevil, Sitophilus zeamais (Motsch) and the house fly, Musca domestica L. The fumigation LC 50 values were calculated by probit analysis. For house flies, all but one of the cyanohydrins tested were more potent than 1,3‐dichloropropene (Telone ® ). Three were as efficacious as chloropicrin. For the lesser grain borer, all cyanohydrins tested were more insecticidal than dichloropropene, and all but one were more potent than chloropicrin. Four were as insecticidal as dichlorvos. The acetate of 1‐cyano‐1‐hydroxy‐2‐propene (CHP‐ace) was also tested in soil for antifungal and antibacterial activity, and inhibition of weed seed germination. CHP‐ace reduced the total soil bacterial and fungal counts significantly, and was effective in inhibiting the germination of weed seeds in soil, indicating a broad spectrum of activity as a soil fumigant. Copyright © 2004 Society of Chemical Industry