A study was made of the Mongolian gerbil, Meriones unguiculatus, to determine its water requirements and ability to utilize salt water. When available, free water is consumed (0.039 grams/gram body weight/day) and weight losses occur when the animals are deprived of water; however, after 29 days without water, body weight appeared to stabilize. Concentrations of salt water up through 0.8 molar could be utilized and some water was even obtained from 1.0 molar.