A total of 1136 Epherneroptera, Plecoptera and Trichoptera were caught from March 1993 to March 1994 at the Weidlingbach, a first to fourth order forest brook near Vienna. Austria, using pyramid-type emergence traps at tree sampling stations (390, 360 and 260 m above sea level). Five species comprised 67.1 % of the catch: the ephemeropterans Puraleptophlebici srrbmtirginuta (STEPHENS), Hirbroleptoides confrrsa SARTORI and J,ACOFI and Hubrophlebia lautu EATON, and the plecopterans Nemoirru jkxuosci AUBERT and Leuctru hippopus KEMPNY.MoSt taxa emerged from April to August, but the plecopterans Leucrra prima KEMPNY and Cupnia bifions (NEWMAN) were caught early in the year (January to April), and Leuctru digitata KEMPNY (Plecoptera), Chuetopteryx frrscii BRAUER and Chcietoptetyx mujor MCLACHLAN (Trichoptera) emerged in September and October. In Ephemeroptera and Trichoptera, similarities between species groups were highest at the two upstream sampling stations; in Plecoptera and in pooled taxa, however, similarities were highest at the middle and downstream sites. Except in Trichoptera, diversity was highest at the middle station situated at 360 m above sea level.