Chlorella vulgaris colonies were grown as nutrient agar for one week, followed by addition of Daphnia magna in overlying water for a second week. A range of concentrations of cadmium were added to the Chlorella or to the Chlorella followed by higher cadmium concentrations in the overlying fluid. A dose-dependent reduction in reproduction was observed with increased cadmium. When parent daphnids were first exposed to a lower cadmium concentration, and their offspring of preconditioned juvenile daphnids then exposed to a higher concentration, cadmium tolerance in new-born daphnids was observed.