Retention values are measured in reverse osmosis and ultra filtration seperation experiments on several salts, hydrocarbons and fertile dyes (reactive dyes; according to table 1). Table 3 shows the used substances and ranges of retention values depending on the feed pressure and concentration. The retentions for salts, dyes, p-nitrophenol and dichlormethane drop in the order of membrane types ROM 104 > ROM 126 > UFM 479 > UFM 545, approximately in the order of increasing permeate fluxes and decreasing pressure driving forces. Experiments performed on p-nitrophenol over the time of one month show a decrease of fluxes of only about 10%. Provided having optimal membranes it will be possible to recycle some reaction and intermediate products from process and waste waters of the dye resp. textile industries with the aim of using the compounds repeatedly in dye synthesis processes or lead to microbiological destruction processes, before and after them.