Megathura crenulata , the giant keyhole limpet, is a relatively common marine invertebrate found in intertidal and subtidal areas along the coast of southern California. There is interest in culturing M. crenulata because its extracellular respiratory pigment, keyhole limpet haemocyanin (known as KLH), is found to have clinical significance. The purpose of this study is to begin to understand how the limpets immune system fights bacterial infections which will hopefully lead to a better understanding of how to culture healthy animals commercially. Five limpets were injected with 10<sup>9</sup> cells of E. coli bacteria mixed with 3% NaCl and five limpets were injected with 10<sup>8</sup> cells of V. fisheri bacteria mixed with 3% NaCl. Blood samples were taken at T0, before injection, and T1, T2, T6, and T24 hours after bacterial injection. Total hemocyte counts were taken for each blood sample and the number of bacteria in the blood was estimated by plating a blood sample and counting colony forming units (CFU?s). The number of bacteria was highest at T1 for both bacterial species ( E. coli x= 9.10 x 10<sup>4</sup> cells/ml; V. fisheri x= 2.11 x 10<sup>4</sup> cells/ml). At two hours after infection the number of bacteria dramatically decreased in the blood system and was completely cleared by 24 hours. These results identify an important timeline in bacterial clearance and will allow for the further study of immune responses in these animals.