The metabolism of trans- and cis-permethrin are studied in rat, cow and insects. The studies utilized eight ¹⁴C-permethrin preparations. Permethrin isomers are rapidly metabolized both hydrolytically and oxidatively. The ester hydrolysis are rapid with trans- than with cis-permethrin from all species. There are species-dependent differences in the preferred sites for hydroxylation of the permethrin isomers and in the conjugation reactions of the metabolites. The parent compound, free metabolites and their conjugates are quickly eliminated from mammals. Decamethrin metabolism in rat is on analogy wtih the metabolism of [IR, cis] permethrin. The cleavage of the decamethrin ester group leads to release of cyanide which is converted mainly to thiocyanate and a small amount of 2-iminothiazolidine-4-carboxylic acid. Allethrin, tetramethrin, resmethrin and furamethrin are included in β-cyclodextrin (CD) in 1:2 molar ratio. The included pyrethroids are stabilized for photodecomposition. The CD inclusion retardes th photochemical attack of the acid moiety for allethrin and of the alcohol moiety for resmethrin. Cochromatographic comparison of the synthetic compounds with the eight metabolites of rotenone confirmed the stereochemical configurations for the metabolites. 2-O-Demethylation is established as a new detoxification mechanism. All the four stereoisomers of natural rotenone and its O-demethyl derivatives are synthesized by the reaction of rotenone and d-epirotenone with one to three equivalents of boron tribromide followed by recyclization of the E-ring. The structure-biological activity relationships of 63 rotenone derivatives including 40 new ones are studied. High potency appears to be associated with the presence of ABCD ring system with the cis-6aβ, 12aβ-B/C ring juncture as in rotenone. Various types of modification of this juncture result in the diminished potency.