An investigation was carried out on the macrobenthos of Montedoglio Reservoir, an artificial lake in central Italy. Seven qualitative and quantitative samplings, performed by drag netting and airlifting at 5 stations, revealed a total of 48 taxa during 1992–94. The highest density and most frequent terms were Tubificidae, Chironomidae of the genera Procladius, Tanypus, Chironomus and Polypedilium and Chaoboridae. Tubificidae were found mainly at a depth of 7–9 m, Chironomidae at 1–3 m. The modest density and low biological diversity values are probably attributable to the substrate characteristics and a drop in hypolymnic oxygen during thermic stratification. The oxygen stress at the lake bed, which was unexpected given the scarce planktonic productivity, may have been caused by recent impoundment.