The Massachusetts population of the northern red-bellied cooter (Pseudemys rubriventris) is listed as federally endangered due to its extremely restricted geographic range and low population. A captive rearing program has been used since 1984 to augment the population. Blood from 30 juvenile specimens from three rearing institutions was collected prior to release, and hematologic and plasma biochemical data were analyzed. Results were generally consistent with previously published data for other species of the family Emydidae. Basophils were the most numerous type of leucocyte. Results for some values varied significantly between institutions, possibly due to unrecognized differences in husbandry at each facility.