In ill cetaceans where electrolytes are monitored it is not uncommon to find that some individuals are hypernatremic, hyperchloremic, and hypokalemic. These abnormalities are sometimes found associated with other symptoms of dehydration such as hemoconcentration and elevated serum protein levels. The differential diagnosis should consider excessive fluid loss (diuresis, diarrhea), increased salt water intake and possibly an aldosterone imbalance. Stomach samples taken from 3 cetaceans with hypernatremia showed ingestion of salt water as the most likely cause when the onset is rapid. Physiologically these animals may appear normal while maintaining sodium levels greater than 185 meq/L. Treatment involves relief of the underlying illness and increased fresh water intake. Increased fresh water intake may be accomplished by oral intubation and by placing the animal in brackish water with a salinity of 14-18 parts per thousand. Animals undergoing therapy for electrolyte imbalances should be monitored every other day during initial stages of therapy. Duration of therapy should be determined by the response with the return to normal levels occurring within 7 - 14 days. Overhydration is possible. A dolphin weighing from 150 - 170 kg can be maintained on 2 liters of water twice a day. Fluid levels contained in fish are usually inadequate as a sole means of hydration in these animals.