A laboratory culture method for the benthic invertebrateChironomus decorusJohannsen is described in detail. The culture requires minimal maintenance and produces an abundant supply of midge larvae throughout the year for many types of bioassays. Appropriate food, substrate, space, photoperiod, and temperature are important aspects of successful midge culture. The life history ofC. decorusis described, and the effects of varying temperature on the time to hatching, larval growth rate, and time to adult emergence were evaluated. Increasing the temperature over the experimental range (10–28°C) decreased the the time to hatch and the time to adult emergence. Larval growth rates increased from 10 to 20°C and declined at higher culture temperatures. Midges cultured at 28°C were half the size of those cultured at lower temperatures. A length/weight regression forC. decoruslarvae cultured at 20°C was calculated.C. decorusis an excellent bioassay organism for both acute and chronic tests because of its relatively short life cycle, wide distribution, ecological importance, and ease of culture in the laboratory. The recommended culture and bioassay temperature forC. decorusis 20°C.