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New insecticides, some in novel formulations, and insect repellents were tested during 1968-71 as seed dressings to protect winter wheat against attack by wheat bulb fly larvae. Preliminary tests in the laboratory were followed by trials in fields in the Midlands and eastern England. The synthetic pyrethroid insecticide resmethrin at one per cent active ingredient to weight of seed significantly decreased attack by wheat bulb fly in one trial on a sandy clay loam but not on other soils or in other years. The best protection against attack in the field was given by the organophosphorus insecticides C8874 (O,O-diethyl O-2,5-dichloro-4-iodophenyl thiophosphate) and C18244 (d-ethyl-O-(2,5-dichloro-4-iodophenyl) ethyl thiophosphonate). These compounds were more effective than chlorfenvinphos used as a standard but are unlikely to be developed further in this country. Using polyvinyl acetate formulations, much larger amounts of pyrethroids could be applied to the seeds without decreasing plant emergence, but insect control was not improved. Pre-treatment with liquid paraffin, 'Lutanol M40' (polyvinyl methyl ether) or 'Polyvis 200' (polybutene) improved adhesion of 7-BHC powder to seed, but effects on plant emergence and on insect control need more testing. A uniform seed to seed distribution of liquid insecticide was obtained by dipping seeds in dilute emulsions of ethion, but these seeds germinated less well than seeds treated with a commercial powder formulation of the same insecticide. Seed dressings of the insect repellents 'Deet' (N,N-diethyl m-toluamide), MGK 11 (2,3:4,5-bis(2-butylene) tetrahydro-2-furaldehyde) or MGK 874 (2-hydroxyethyl-n-octyl sulphide) failed to protect winter wheat from attack by wheat bulb fly in the field. [ABSTRACT FROM AUTHOR]