The concentrations of Cd, Pb, Cu and Zn in Chironomus gr. thummi were determined for 4th instar larvae from the polluted Dyle River, tributary of the Scheldt River (Belgium). Comparison was made between larvae with deformed and normal menta. Deformed larvae showed higher overall metal concentrations than normal larvae. Especially Pb and Cu had higher concentrations in deformed larvae (16.22 mg kgdry weight and 39.66 respectively) than in normal larvae (12.80 mg kg-1 dry weight and 35.70 respectively). No significant differences were found in the concentrations of Cd and Zn (mean [Cd] = 0.81 mg kg-1 dry weight and mean [Zn] = 313.12 mg kg-1 dry weight). There was no difference between the two larval groups as far as total length, dry weight and developmental stage of the imaginal discs are concerned.