A study on the horizontal distribution of rotifers (Rotifera) and crustaceans (Cladocera and Copepoda) was conducted in Lake Budzyńskie, located in Wielkopolski National Park, Poland. Zooplankton was sampled six times within 24 hours (31 August-1 September, 1996) from five stations. These were located in a zone of rushes, two zones of submerged macrophytes (Chara and Myriophyllum) and two areas of free water between the vegetation beds. It was observed that the diurnal horizontal distribution of particular groups of zooplankton differs, mostly depending on the particular species of macrophyte. The highest numbers of both rotifers and crustaceans were recorded for the Myriophyllum verticillatum zone, irrespective of the time of the day.