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The glucosinolates of a Saharan crucifer Schouwia purpurea (Forskal) (Brassicaceae) were determined by liquid chromatography. Two of these glucosinolates and sinigrin were tested for their deterrent effect on Schistocerca gregaria (Forskal) (Orthoptera: Acrididae). Glucobrassicin, three indolyls and epigoitrin were synthesized for this purpose. Epiprogoitrin was extracted from Crambe seeds. Choice tests on artificial substrate compared feeding responses to glucosinolates and to related breakdown products released when the plant is eaten. Breakdown products were more efficient in deterring the generalist locust than were glucosinolates. Two patterns of dose responses were recorded: glucosidic compounds deterred or stimulated feeding, depending on the concentration tested; aglycones did not stimulate feeding at any concentration. Allyl isothiocyanate, a volatile compound, was a 100-fold higher deterrent than its substrate (sinigrin).