An aqueous biocidal composition containing: Alcohols and Paraffins and detergents as additives and one or more pyrethroids, like Allethrins, Allethrin stereoisomers, Bifenthrin, Beta-Cyfluthrin, Cyfluthrin, Cypermethrin, Cyphenothrin, Deltamethrin, Derivative of Pyrethrin, Dichlorovinyl, Esfenvalerate, Etofenprox, Fenpropathrin, Fenvalerate, Flumethrin, Flucythrinate, Tau-Fluvalinate, Imiprothrin, Lambda-Cyhalothrin, Gamma Cyhalothrin, Imiprothrin, Metofluthrin Permethrin, 1RS cis-Permethrin, Permethrin, Prallethrin, Resmethrin, Silafluofen, Sumithrin (d-phenothrin), Tefluthrin, Tetramethrin, Tralomethrin, Transfluthrin, Zeta-Cypermethrin and any other existing type I and type II pyrethroids, as well as any other type I and type II pyrethroids to be developed in the future, as active ingredients. The invention is that this composition has a stabilizing and prolonging effect on the efficacy of the pyrethroids together with a very excellent risk-benefit ratio, i.e. a high toxicity to target organisms and low risk to humans and warm-blooded animals. Variations of the basic compositions can be used for a wide-variety of biocidal applications in sectors like agriculture, household, industrial, animal care, repellent, veterinary, construction, wood preservation, personal hygiene, gardening, monument conservation. This composition can further be combined with synergists like Piperonylbutoxide for further increase of biocidal activity for special applications, but also with colorants, fragrances and skin care oils especially for veterinary use and use as human repellent. If the additives are mixed in selected ratios the stabilizing effect is especially significant. In the same way combination ratios of the active ingredients contribute to the biocidal activity and stability of the products. The invention is suitable for the pest control of arthropods like insects and arachnoids and nematodes. To the above species belong: lice, mosquitoes, cockroaches, beetles, flies, i.e. m
