Feeding and production rates of the freshwater rotifer, B. calyciflorus Pallas, were determined during a daily cycle of feeding with the alga Dictyosphaerium chlorelloides or with the yeast Saccharomyces cerevisiae. Filtration and ingestion rates of rotifers decreased significantly during the cycle of feeding. The filtration rate decreased from 4.02 to 1.18 μl/ind. h-1 with the algae and from 2.06 to 0.94 μl/ind. h-1 with the yeast. Production rates of 28 and 17 ind./ml d-1 were achieved, respectively, with algae and yeast. The filtration rate of rotifers was significantly influenced by the cellular density of algae but not by that of yeast. The maximal value (4.04 μl/ind. h-1) was obtained at an algal density of 4 × 106 cell/ml. With algae, the ingestion rate seemed to reach a maximum between 4 and 8 × 106 cell/ml (191 × 102 cell/ind. h-1) at 5 × 106 cell/ml. With yeast, the rotifer ingested a maximum of 86 × 102 cell/h. At optimal cellular density and photoperiod (L:D 24:0), the filtration and ingestion rates of rotifers were maximal at 25 °C.