What effects will elevated ultraviolet B radiation and/or elevated temperature have on the loss of zooxanthellae from Aiptasia pallida? The hypothesis of this study was: if Aiptasia pallida are exposed to elevated ultraviolet radiation and/or elevated water temperatures, then the number of zooxanthellae expelled from the Aiptasia pallida will increase. Sea anemones (Aiptasia pallida) containing symbiotic zooxanthellae (Symbiodinium bermudense) were maintained in 3 L salt-water aquariums on a 10:14 hour light:dark cycle. In addition to a control aquarium, one aquarium was exposed to elevated water temperature, another aquarium was exposed to elevated UVB radiation, and the fourth aquarium was exposed to elevated levels of both UVB radiation and water temperature. The number of zooxanthellae expelled from the sea anemones was measured with a hemacytometer once every three days over a fifteen-day period. The number of zooxanthellae expelled per sea anemone was lowest in the control aquarium. The number of zooxanthellae expelled per sea anemone was greatest in the aquarium that was exposed to elevated levels of both UVB radiation and water temperature. Aquariums that were exposed to elevated levels of either UVB radiation or water temperature experienced moderate levels of expulsion. In conclusion, elevated levels of both UVB radiation and water temperature had a greater effect on the loss of symbiotic zooxanthellae than the effect of either variable individually or the control.