The effects of feeding Daphnia magna on algae (Scenedesmus acutus) pretreated with different concentrations of Cr(VI) were studied. A positive effect on growth and newborn production rate was observed in the daphnids fed on algae exposed to 1 mg/liter Cr(VI). Fecundity and growth were drastically reduced in daphnids fed on algae exposed to 10 mg/liter Cr(VI). Since the algae, cultured in the presence of these two Cr(VI) concentrations, supplied daphnids with similar amounts of chromium, the observed effects on the population dynamics of D. magna were attributed more to alterations of the nutritional value of the algal food, due to the Cr treatment, than to a toxic effect of the metal.