The concentrations of some nonvolatile halogenated hydrocarbons in surface waters of an industrialized city and its surroundings are given. About 80% of the ballast isomers of hexachlorocyclohexane (alpha, beta and delta BHC) and of DDT and its metabolites are in the range of less than 5 micrograms l-1, whereas ca. 50% of lindane (gamma BHC) were found to be between 5 and 100 micrograms l-1. Starting form the remarks about the differential-diagnostic assessment of environmental concentrations conclusions as to the origin of hexachlorocyclohexane isomers are drawn with the help of their distribution pattern. A high part of the gamma isomer, compared with the ballast isomers means an application (e.g. against mosquitos). This fact may be supported if it coincides with the months typical for such an application. in contrast to this if you have high percentages of alpha, beta and delta hexachlorocyclohexane, it indicates a point source or diffuse inputs of technical BHC. If all four isomers are present on a comparable and very low level this may reflect a remobilization from the sediment.