Ninety-six hour, static acute, and continuous-flow early life-stage (ELS) chronic toxicity tests, using the fathead minnow (Pimephales promelas), were conducted to evaluate the toxicity of effluents from a pilot scale activated sludge (AS) treatment system receiving dye and pigment wastewater. In the first test with a powdered activated carbon (PAC) dosage of 1800 mg/L of influent, survival was the most sensitive measure of effect in the ELS test. The highest effluent concentration tested (10%) was lethal to the embryos and larvae. No adverse effect on survival or growth was observed at lower effluent concentrations (5.0 to 0.63%). The maximum acceptable toxicant (effluent) concentration (MATC) was between 10 and 5%. Ten 96-h median lethal concentration (LC₅₀) values from static acute tests ranged from 12.9 to greater than 80%. In the second test at a PAC dosage of 1000 mg/L of influent, growth was the most sensitive measure of effect in the ELS test. Larval growth was significantly reduced at the highest effluent concentration tested (20%). The MATC was between 20 and 10%. Seven 96-h LC_50s from static acute tests ranged from 28.3 to greater than 80%. The effluent from the treatment system receiving the higher PAC dosage of 1800 mg/L was more toxic than the effluent from the treatment system receiving the lower PAC dosage of 1000 mg/L. However, the influent to the treatment system receiving the higher level of PAC also was more acutely toxic.