The two enantiomers of the insecticide fipronil were made by preparative HPLC. The insecticidal activities of the racemic mixture and the two enantiomers against selected agricultural or household pests (cotton stainer, Dysdercus cingulatus F; grain weevil, Sitophilus granarius L and house fly, Musca domestica L) were determined. There was no significant difference in acute or residual activity between the racemic mixture and the enantiomers of fipronil, indicating that there is no preferred chiral form of the compound in these key species of important insects. This observation clearly suggests that there is no major scope for marketing the insecticide in a one-enantiomer form.