Alkylated amidines dissolved in an aromatic hydrocarbon were absorbed in macro-porous polystyrene beads to form a water-immiscible extractant system for the removal of nitrate from wastewaters. The amidines are relatively strong bases and possess the advantage over the simple aliphatic amines that they exist in the salt form in contact with wastewaters in the pH range of 7.0 to 8.0. They can, however, be readily regenerated with alkalis, such as ammonia or sodium hydroxide. Amidinium ion in the organic phase selectively extracts nitrate ion over chloride ion by a factor of about 20 (nitrate/chloride ratio in the organic phase is about 20 times the ratio in the equilibrium aqueous phase), and nitrate over sulfate and bicarbonate by much higher ratios. Therefore, amidine systems will pick up mainly nitrate ion from municipal wastes. Seventy bed volumes of a synthetic municipal wastewater containing 62 ppm nitrate ion and 350 ppm chloride ion were treated before breakthrough of nitrate ion in the effluent. Processing costs were estimated currently at 16 cents/1000 gal.