The use of Chironomidae in the biomonitoring of fresh waters is reviewed. Examples are given for levels of organization from organism to ecosystem, and a separate consideration is devoted to toxicity studies. Morphological deformities and life-history responses of Chironomidae to contaminants are common organism-level indicators. At the species-assemblage level, the classic lake trophic classification scheme, its contemporary derivatives, and paleolimnological approaches have been used extensively. Chironomidae also are essential components of quantitative and qualitative (rapid assessment) community approaches to biomonitoring. Examples of chironomids as components of ecosystem-level studies are rare, but even the few studies done show their value for this purpose. In toxicity testing, Chironomidae frequently are used in single species acute, single species chronic, and multispecies tests for a variety of stressors; Chironomidae could be used profitably in any expansion of toxicity testing involving macroinvertebrates. The review indicated that more emphasis on Chironomidae is required in studies of biochemical and physiological indicators of contaminants (organism level), and on Chironomidae as sentinel organisms (population level). Extensive use of Chironomidae in biomonitoring of fresh waters is consistent with the abundance and taxa richness of this group in natural habitats.