Crayfish exhibit innate immune responses via hemocytes and their products. There are 3 hemocyte populations: hyaline cells, granular cells, and semigranular cells. Hemocytes from laboratory housed, untreated crayfish (normal crayfish) have been quantified on the basis of cell type, cell size, and cell granularity using Flow Cytometry. These data present the first overall picture of normal hemocytes from Red Swamp Crayfish with regard to cell type, cell size, and cell granularity and will serve as a baseline for all future studies in our lab. Experiments using crayfish injected with Pseudomonas aeruginosa, Staphylococcus aureus, or crayfish saline alone showed significant and consistent changes in cell type in cells from crayfish injected with bacteria with a decrease in hyaline cells and an increase in granular cells. This effect was greater in crayfish injected with Gram - bacteria. In addition, crayfish injected with Pseudomonas aeruginosa showed a significant difference in Granular cell size with a shift to larger cells and a significant decrease in granularity in the Granular cell population. Cells from crayfish treated with Staphylococcus aureus did not show these changes.