Resistance of field strains of Oryzaephilus surinamensis L. (sawtoothed grain beetle) to grain protectants was assessed using commercial dose rates of protectant in treated grain bioassays. Grain protectants tested were: chlorpyrifos- methyl, 5 and 10 mg/kg grain; methacriphos, 10 and 18 mg/kg; pirimiphos-methyl 4 mg/kg; fenitrothion, 12 mg/kg, plus carbaryl, 8 mg/kg; fenitrothion, 12 mg/kg, plus bioresmethrin, 1 mg/kg, plus piperonyl butoxide, 8 mg/ kg; pyrethrins, 3 mg/kg, plus piperonyl butoxide, 24 mg/kg. About 10% of farms surveyed and about 42% of merchant premises were infested. Most of the insects originating from farms were effectively controlled by all grain protectants. However, some strains showed less than 100% adult mortality and some progeny production when treated with: chloropyrifos-methyl at 5 mg/kg; pirimiphos-methyl; and pyrethrins plus piperonyl butoxide. In contrast, for all strains obtained from the premises of grain merchants, none of the grain protectants, except methacrifos at 18 mg/kg, caused complete adult mortality whilst fenitrothion, chlorpyrifos-methyl at 5 mg/kg and pyrethrins plus piperonyl butoxide failed to completely suppress progeny production in some strains. A composite strain showed no mortality with fenitrothion at 12 mg/kg after five generations of laboratory selection.