Daphnia, commonly known as water fleas, are small aquatic crustaceans that are an important link between aquatic primary production and small fish and other invertebrate species. Their role in the environment may be adversely impacted by the presence of agrichemicals. Two pesticides of concern within the Indian River area (east coast of Florida) are aldicarb and copper. Aldicarb and copper are primarily used in citrus production within the region. Aldicarb is applied to control insects, mites, and nematodes, and copper is a fungicide. These pesticides have been detected in local waterways, sometimes simultaneously, at concentrations ranging from 0.16 to 4.97mg/L and 0.12 to 45mg/L respectively. Because of the different modes of action on non-target organisms, it is possible that exposure of Daphnia to these pesticides in combination may lessen their ability to survive relative to exposure to each pesticide individually. The effects of aldicarb and copper exposure were first tested individually on Daphnia pulex. Neonates less than 24 hours old were exposed to a range of nominal concentrations to determine the concentration lethal to 50 percent of the population. The neonate mortality was observed after 24 and 48 hours. At 24 and 48 hours, the LC50s for alidcarb were 241.6 mg/L and 118.8 mg/L, respectively. For copper, the LC50s at 24 and 48 hours were 3.5 mg/L and 2.4 mg/L, respectively. After normalizing concentrations to toxic units (one toxic unit = LC50 for each pesticide), neonates were then exposed to aldicarb and copper simultaneously at 0.5, 0.75, 1.0, 1.5, and 2.0 toxic units. The LC50s observed were 1.8 and 1.5 toxic units after 24 and 48 hours, respectively, indicating that the chemicals may not be synergistic in combination.