Twelve adult male corn snakes, Pantherophis (Elaphe) guttatus guttatus, were used for this study. Blood samples were collected via cardiocentesis or caudal tail venipuncture. Plasma chemistries were measured using a standard laboratory chemistry analyzer; these parameters were used to calculate plasma osmolality. Osmolality also was measured using a freezing point osmometer. The osmolality measured with the osmometer in the corn snakes ranged from 304.5 to 373.0 mOsm/kg, with a mean value of 344.5 mOsm/kg. These values are higher than the osmolality of Ringer's solution (310 mOsm/L), lactated Ringer's solution (272 mOsm/L), Plasma-Lyte A^® (294 mOsm/L), and Normosol R^® (295 mOsm/L) and should be taken into account when replenishing fluids to avoid large shifts in plasma osmolality. Bland Altman plots were used to assess the level of agreement between the measured and calculated osmolalitites. The results of the comparisons showed the highest level of agreement between the measured and calculated osmolality when using the following formula: (2 × [Na K ]) (glucose concentration/18). Two other formulas, 2 × (Na K ) and 2 × [Na K ] (glucose concentration/18) (uric acid/16.8), likewise showed good agreement with the measured osmolality. One formula, 2 × Na , showed a fair level of agreement with the measured osmolality. Additional studies are needed in snakes to investigate fluid replacement using commercially available crystalloid fluids, develop appropriate isotonic fluids, and evaluate osmolality as changes in hydration status occur in healthy and unhealthy animals.