The toxicity of an ozonated, secondary-treated municipal waste effluent to bluegill sunfish was investigated in a continuous-flow bioassay system. Four bioassay experiments were conducted, one with untreated secondary effluent and three with ozonated, secondary effluent. Ozone was applied at dosages between 12.1 and 52.0 mg/l for contact times between five and ten minutes. Several waste parameters were measured periodically throughout the investigation to determine the effects of ozonation on the secondary-treated effluent. No toxicity was demonstrated during any of the bioassays. Analytical data demonstrated that ozone treatment of secondary effluents resulted in large reductions in color, but only small reductions in COD. Increases in pH and ammonia nitrogen concentrations were observed. / Master of Science