As EC validity criteria for the production of Daphnia magna neonates in standard toxicity tests set fecundity minima which must be attained, it is important that culture conditions provide an adequate ration of high quality food. Maintaining a steady supply of fresh algae can be problematical so the possibility of using frozen food was investigated. The performance of three generations of D. magna fed on diets of fresh or frozen Chlorella was compared. There were no significant effects on fecundity due to food type or generation. Cumulative fecundity (over 21 days) on fresh or frozen food exceeded 120 neonates per female and satisfied that EC validity criterion (60 neonates per female). In addition criteria relating to survival and variability were met. We conclude that frozen Chlorella are an acceptable substitute for fresh algae.