Since the first finding in 1853 (Frivaldszky, 1865), 27 Amphipoda have been reported from Hungary, half of them being Niphargus species. The other amphipod species belong to the genera Gammarus, Dikerogammarus, Echinogammarus, Corophium, Synurella, Orchestia, and Talitrus. The most detailed data are available from Lake Balaton where altogether 8 species were found in different habitats, only a few species occurring together. In the 1930s Corophium curvispinum invaded Lake Balaton. This species was reported from Hungary for the first time in 1916 (from the Danube). In the 1950s Dikerogammarus species replaced Gammarus roeselii in the lake. We investigated the ecology of the Amphipoda fauna in Lake Balaton from 1983 to 1987. Both on the submerged macrophytes and in the stony littoral zone of Lake Balaton Corophium curvispinum, Dikerogammarus haemobaphes, and Dikerogammarus villosus occur, with dominancy of Corophium curvispinum. C. curvispinum and D. haemobaphes, living on the submerged macrophyte Myriophyllum spicatum near Tihany peninsula, reproduce in late spring, summer, and early autumn. They produce two generations a year. The biomass of C. curvispinum and D. haemobaphes was roughly 11 and 0.1 g animal dry wt.m -2 , respectively, in mid-July 1986, in areas covered by Myriophyllum spicatum.