Pfiesteria piscicida Steidinger & Burkholder, an estuarine dinoflagellate known to kill fish, has also been associated with neurocognitive deficits in humans. We have developed a rat model to determine the cause-and-effect relationship between exposure to Pfiesteria-containing water and cognitive impairment and to determine the neurobehavioral mechanisms underlying the Pfiesteria effect. The rat model of Pfiesteria toxicity can also provide important information concerning the toxin or toxins responsible for neurocognitive deficits resulting from Pfiesteria exposure. With the rat model we have repeatedly documented a Pfiesteria-induced choice accuracy impairment during radial-arm maze learning. The Pfiesteria-induced impairment was relatively specific to the acquisition phase of training. When rats were pretrained, Pfiesteria treatment did not affect performance. However, when these same rats were retrained on another task, the Pfiesteria-induced impairment became evident. Pfiesteria-induced effects were also seen in a locomotor activity test in the figure-8 apparatus and selected components of the functional observational battery. Pfiesteria effects on choice accuracy in the radial-arm maze in rats constitute a critical component of the model of Pfiesteria toxicity, as the hallmark of Pfiesteria toxicity in humans is cognitive dysfunction. Our finding that analysis of the first six sessions of radial-arm maze testing is sufficient for determining the effect means that this test will be useful as a rapid screen for identifying the critical neurotoxin(s) of Pfiesteria in future studies.