The four larval instars of the midge Chironomus tentans Fabricius were exposed to copper to determine their relative sensitivities. The impact of copper on adult emergence and effect of exposure time on LC50 values were also determined. First-instar larvae appeared to be the most sensitive to acute exposure, with a 96-h LC50 of 298 micrograms/L copper, followed by second-instar (LC50=773 micrograms/L), third-instar (LC50=1690 micrograms/L) larvae, at a water hardness of 71 to 84 mg/L. Adults emerged successfully from fourth-instar larvae and pupae that survived 20-D copper exposures of up to 235 micrograms/L; the 20-day EC50 was 77.5 micrograms/L. Methods for continuous culture of C. tentans in a flow-through rearing facility using Cerophyl, a commercially available powdered grass product, as food and substrate are presented.