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 treatment system receiving dyes and pigments wastewater. In the first test with a powdered activated carbon (PAC) dosage of 1800 mg/litre of effluent, survival was the most sensitive measure of effect in the ELS test. The highest effluent concentration tested (10 percent) was lethal to the embroyos and larvae. No adverse effect on survival or growth was observed at lower effluent concentrations (5.0-0.63 percent). The maximum acceptable toxicant (effluent) concentration (MATC) was between 10 and 5 percent. Ten 96-h median lethal concentration (LC50) values from static acute tests ranged from 12.9 to greater than 80 percent. In the second test at a PAC dosage of 1000 mg/litre of effluent, growth was the most sensitive measure of effect in the ELS test. Larval growth was significantly reduced at the highest effluent concentration tested (20 percent).