Sample preparation can be used in biology and ecology for gas chromatographic determination of organochlorine pesticides (OCP), namely, α-, β- and γ-isomers of hexachlorocyclohexane (HCH), dichlorodiphenyltrichloroethane (DDT) and its metabolites dichlorodiphenyldichloroethane (DDD) and dichlorodiphenyldichloroethylene (DDE) in various aquatic organisms (molluscs, fish, birds and mammals) containing lipids (because organochlorine pesticides are lipophilic) in the internal organs and tissues, fat, skin and feather cover. The method is easy to implement and economically profitable; it can be used in laboratories without special extraction equipment, as well as in the field, with a minimum set of glassware and reagents. The result of this process is an increase of efficiency and precision of research through a more complete extraction of pesticides chemically bonded with lipids using n-hexane and a reduction of the number of steps needed for the extraction and purification of co-extrusive substances with concentrated sulphuric acid