This document specifies a method for the determination of the toxic values of a wood preservative against the larvae of Hylotrupes bajulus (Linnaeus), introduced into wood treated previously by full impregnation. This method is applicable to: water-insoluble chemicals which are being studied as active insecticides; organic formulations, as supplied or as prepared in the laboratory by dilution of concentrates; organic water-dispersible formulations as supplied or as prepared in the laboratory by dilution of concentrates; and water-soluble materials, for example salts. The method is applicable whether or not the test specimens have been subjected to appropriate ageing procedures.