Flow cytometry provides a rapid and reproducible method for analyzing crustacean hemocytes and their functions under experimentally-varied environmental conditions. We used flow cytometry to determine if there was a difference in hematology and selected immune functions, and intracellular pH (pHi), under two different, future ocean acidification scenarios (pH = 7.51, 7.80) compared to current conditions (pH = 8.06) for Chionoecetes bairdi, the Tanner crab. Hemocytes were analyzed after adult Tanner crabs were held for two years under continuous exposure to acidified ocean water. Total counts of hemocytes did not vary among experimental control and treatments; however, there was a significantly greater number of dead, circulating hemocytes in crabs held at the lowest pH treatment. Phagocytosis of fluorescent microbeads by hemocytes was greatest at the lowest pH treatment. These results suggest that hemocytes were dying, likely by apoptosis, at a rate faster than upregulated phagocytosis was able to remove moribund cells from circulation at the lowest pH. There was no significant difference in pHi within hyalinocytes among pH levels, with apparent regulation to a mean pHi of 7.24, significantly lower than the external environment. In contrast, there was a significant difference between treatments in pHi of the semi-granular+granular cells. These findings suggest that future, predicted levels of ocean acidification may affect the defense cells of Tanner crabs, possibly making them more susceptible to other stressors in the environment.