-The reactions of hetero-tricyclic aromatic hydrocarbons (H-TCAHs) with hypochlorite in an aqueous solution were investigated under conditions that simulate wastewater disinfection. H-TCAH-hypochlorite reaction products were determined by gas chromatographic-mass spectrometric (GC-MS) analyses. For 20 µM, 10H-phenothiazine, 10H-phenoxazine, and phenoxathiin reacted rapidly with active chlorine in neutral pH (7.0), but no phenazine-hypochlorite reaction was observed over pH values of 5-9 for 1 hr. The 10H-phenothiazine-hypochlorite reaction began by oxidation with active chlorine to form its dioxides, followed by chloro-substitution in water. The extent of the reactions depended on the chlorine dose, solution pH and compound structures. Ames assays for the chlorination byproducts of 10H-phenothiazine and 10H-phenoxazine also showed to be weak mutagenicity in TA98 and TA100 strains without S9 mix, but no chlorination byproducts of phenoxathiin exhibited any mutagenicity in both tester strains with and without S9 mix.