Filtration rate (F) and ingestion rate (I) were measured in the rotifer B. plicatilis feeding on the flagellate Dunaliella spec. and on yeast cells (Saccharomyces cerevisiae ). 60-min experiments in rotating bottles servedas a standard for testing methodological effects on levels of F and I. A lack of rotation reduced F values by 40%, and a rise in temperature from 18 degree to 23.5 degree C increased them by 42%. Ingestion rates increased significantly up to a particle (yeast) concentration of ca. 600-800 cells/µl; then they remained constant, whereas filtration rates decreased beyond this threshold. Elemental analyses ofrotifers and their food suggest that B. plicatilis can ingest up to 0.6 mJ or ca. 14% of its own body carbon within 15 min. The long term average was estimated as 3.4 m/ind or ca. 75% of body carbon/d.